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 $82.90   12.721%   $93.4457   $93.45   $93.45   $93.40  
  Purchase #2 $245.55   7.300%   $263.4752   $263.48   $263.50   $263.50  
  Purchase #3 $170.26   6.866%   $181.9501   $181.95   $181.95   $182.00  
  Purchase #4 $174.83   11.335%   $194.647   $194.65   $194.65   $194.60  
  Purchase #5 $141.33   8.245%   $152.9827   $152.98   $153.00   $153.00  
  Purchase #6 $115.98   8.148%   $125.4301   $125.43   $125.45   $125.40  
  Purchase #7 $57.87   6.795%   $61.8023   $61.80   $61.80   $61.80  
  7 purchase totals = $988.72       $1,073.7331   $1,073.74   $1,073.80   $1,073.70