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 $77.62   10.200%   $85.5372   $85.54   $85.55   $85.50  
  Purchase #2 $103.37   13.390%   $117.2112   $117.21   $117.20   $117.20  
  Purchase #3 $208.72   13.380%   $236.6467   $236.65   $236.65   $236.60  
  Purchase #4 $165.32   5.109%   $173.7662   $173.77   $173.75   $173.80  
  Purchase #5 $55.86   8.723%   $60.7327   $60.73   $60.75   $60.70  
  Purchase #6 $118.45   5.747%   $125.2573   $125.26   $125.25   $125.30  
  Purchase #7 $174.39   13.237%   $197.474   $197.47   $197.45   $197.50  
  7 purchase totals = $903.73       $996.6253   $996.63   $996.60   $996.60