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 $42.47   3.610%   $44.0032   $44.00   $44.00   $44.00  
  Purchase #2 $173.84   12.716%   $195.9455   $195.95   $195.95   $195.90  
  Purchase #3 $201.90   9.394%   $220.8665   $220.87   $220.85   $220.90  
  Purchase #4 $235.34   3.439%   $243.4333   $243.43   $243.45   $243.40  
  Purchase #5 $46.69   10.668%   $51.6709   $51.67   $51.65   $51.70  
  Purchase #6 $40.69   6.423%   $43.3035   $43.30   $43.30   $43.30  
  Purchase #7 $239.69   5.831%   $253.6663   $253.67   $253.65   $253.70  
  7 purchase totals = $980.62       $1,052.8892   $1,052.89   $1,052.85   $1,052.90