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 $86.75   9.208%   $94.7379   $94.74   $94.75   $94.70  
  Purchase #2 $40.56   12.476%   $45.6203   $45.62   $45.60   $45.60  
  Purchase #3 $118.52   7.347%   $127.2277   $127.23   $127.25   $127.20  
  Purchase #4 $50.95   11.436%   $56.7766   $56.78   $56.80   $56.80  
  Purchase #5 $32.78   11.523%   $36.5572   $36.56   $36.55   $36.60  
  Purchase #6 $221.74   3.274%   $228.9998   $229.00   $229.00   $229.00  
  Purchase #7 $199.96   8.832%   $217.6205   $217.62   $217.60   $217.60  
  7 purchase totals = $751.26       $807.5400   $807.55   $807.55   $807.50