Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $163.97   10.564%   $181.2918   $181.29   $181.30   $181.30  
  Purchase #2 $119.35   13.412%   $135.3572   $135.36   $135.35   $135.40  
  Purchase #3 $209.30   12.394%   $235.2406   $235.24   $235.25   $235.20  
  Purchase #4 $173.26   6.366%   $184.2897   $184.29   $184.30   $184.30  
  Purchase #5 $125.98   12.538%   $141.7754   $141.78   $141.80   $141.80  
  Purchase #6 $182.42   8.257%   $197.4824   $197.48   $197.50   $197.50  
  Purchase #7 $194.35   13.306%   $220.2102   $220.21   $220.20   $220.20  
  7 purchase totals = $1,168.63       $1,295.6473   $1,295.65   $1,295.70   $1,295.70