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 $63.79   3.346%   $65.9244   $65.92   $65.90   $65.90  
  Purchase #2 $104.69   13.342%   $118.6577   $118.66   $118.65   $118.70  
  Purchase #3 $75.81   11.515%   $84.5395   $84.54   $84.55   $84.50  
  Purchase #4 $217.42   13.575%   $246.9348   $246.93   $246.95   $246.90  
  Purchase #5 $250.73   13.499%   $284.576   $284.58   $284.60   $284.60  
  Purchase #6 $97.70   6.676%   $104.2225   $104.22   $104.20   $104.20  
  Purchase #7 $51.55   3.337%   $53.2702   $53.27   $53.25   $53.30  
  7 purchase totals = $861.69       $958.1251   $958.12   $958.10   $958.10