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 $186.66   7.680%   $200.9955   $201.00   $201.00   $201.00  
  Purchase #2 $31.29   8.466%   $33.939   $33.94   $33.95   $33.90  
  Purchase #3 $47.51   7.245%   $50.9521   $50.95   $50.95   $51.00  
  Purchase #4 $227.35   12.154%   $254.9821   $254.98   $255.00   $255.00  
  Purchase #5 $75.57   4.790%   $79.1898   $79.19   $79.20   $79.20  
  Purchase #6 $71.97   4.146%   $74.9539   $74.95   $74.95   $75.00  
  Purchase #7 $71.26   6.770%   $76.0843   $76.08   $76.10   $76.10  
  7 purchase totals = $711.61       $771.0967   $771.09   $771.15   $771.20