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 $60.52   7.248%   $64.9065   $64.91   $64.90   $64.90  
  Purchase #2 $178.97   9.237%   $195.5015   $195.50   $195.50   $195.50  
  Purchase #3 $193.38   7.634%   $208.1426   $208.14   $208.15   $208.10  
  Purchase #4 $36.60   5.327%   $38.5497   $38.55   $38.55   $38.50  
  Purchase #5 $102.75   3.725%   $106.5774   $106.58   $106.60   $106.60  
  Purchase #6 $41.84   3.179%   $43.1701   $43.17   $43.15   $43.20  
  Purchase #7 $197.79   6.728%   $211.0973   $211.10   $211.10   $211.10  
  7 purchase totals = $811.85       $867.9451   $867.95   $867.95   $867.90