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 $241.77   8.598%   $262.5574   $262.56   $262.55   $262.60  
  Purchase #2 $94.97   8.402%   $102.9494   $102.95   $102.95   $102.90  
  Purchase #3 $85.90   4.468%   $89.738   $89.74   $89.75   $89.70  
  Purchase #4 $94.54   9.317%   $103.3483   $103.35   $103.35   $103.30  
  Purchase #5 $171.72   13.803%   $195.4225   $195.42   $195.40   $195.40  
  Purchase #6 $25.84   6.793%   $27.5953   $27.60   $27.60   $27.60  
  Purchase #7 $135.73   5.715%   $143.487   $143.49   $143.50   $143.50  
  7 purchase totals = $850.47       $925.0979   $925.11   $925.10   $925.00