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 $82.57   7.219%   $88.5307   $88.53   $88.55   $88.50  
  Purchase #2 $26.94   8.571%   $29.249   $29.25   $29.25   $29.20  
  Purchase #3 $27.83   13.229%   $31.5116   $31.51   $31.50   $31.50  
  Purchase #4 $60.35   13.476%   $68.4828   $68.48   $68.50   $68.50  
  Purchase #5 $189.75   12.518%   $213.5029   $213.50   $213.50   $213.50  
  Purchase #6 $142.67   9.531%   $156.2679   $156.27   $156.25   $156.30  
  Purchase #7 $169.34   3.664%   $175.5446   $175.54   $175.55   $175.50  
  7 purchase totals = $699.45       $763.0895   $763.08   $763.10   $763.00