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 $63.97   10.378%   $70.6088   $70.61   $70.60   $70.60  
  Purchase #2 $197.38   6.172%   $209.5623   $209.56   $209.55   $209.60  
  Purchase #3 $131.60   9.298%   $143.8362   $143.84   $143.85   $143.80  
  Purchase #4 $182.82   8.227%   $197.8606   $197.86   $197.85   $197.90  
  Purchase #5 $81.59   11.536%   $91.0022   $91.00   $91.00   $91.00  
  Purchase #6 $33.97   9.344%   $37.1442   $37.14   $37.15   $37.10  
  Purchase #7 $56.64   10.592%   $62.6393   $62.64   $62.65   $62.60  
  7 purchase totals = $747.97       $812.6536   $812.65   $812.65   $812.60