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 $38.27   13.343%   $43.3764   $43.38   $43.40   $43.40  
  Purchase #2 $179.73   10.137%   $197.9492   $197.95   $197.95   $197.90  
  Purchase #3 $37.58   6.132%   $39.8844   $39.88   $39.90   $39.90  
  Purchase #4 $231.50   13.646%   $263.0905   $263.09   $263.10   $263.10  
  Purchase #5 $87.88   5.793%   $92.9709   $92.97   $92.95   $93.00  
  Purchase #6 $249.48   7.633%   $268.5228   $268.52   $268.50   $268.50  
  Purchase #7 $14.96   9.292%   $16.3501   $16.35   $16.35   $16.40  
  7 purchase totals = $839.40       $922.1443   $922.14   $922.15   $922.20