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 $78.95   4.613%   $82.592   $82.59   $82.60   $82.60  
  Purchase #2 $202.86   3.358%   $209.672   $209.67   $209.65   $209.70  
  Purchase #3 $197.34   13.556%   $224.0914   $224.09   $224.10   $224.10  
  Purchase #4 $98.84   9.355%   $108.0865   $108.09   $108.10   $108.10  
  Purchase #5 $159.55   9.457%   $174.6386   $174.64   $174.65   $174.60  
  Purchase #6 $72.78   12.479%   $81.8622   $81.86   $81.85   $81.90  
  Purchase #7 $42.81   13.350%   $48.5251   $48.53   $48.55   $48.50  
  7 purchase totals = $853.13       $929.4678   $929.47   $929.50   $929.50