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 $32.71   11.172%   $36.3644   $36.36   $36.35   $36.40  
  Purchase #2 $217.64   8.489%   $236.1155   $236.12   $236.10   $236.10  
  Purchase #3 $109.25   10.307%   $120.5104   $120.51   $120.50   $120.50  
  Purchase #4 $25.93   5.341%   $27.3149   $27.31   $27.30   $27.30  
  Purchase #5 $216.85   4.446%   $226.4912   $226.49   $226.50   $226.50  
  Purchase #6 $243.34   3.221%   $251.178   $251.18   $251.20   $251.20  
  Purchase #7 $131.52   7.208%   $141   $141.00   $141.00   $141.00  
  7 purchase totals = $977.24       $1,038.9744   $1,038.97   $1,038.95   $1,039.00