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 $85.57   9.406%   $93.6187   $93.62   $93.60   $93.60  
  Purchase #2 $59.42   9.302%   $64.9472   $64.95   $64.95   $64.90  
  Purchase #3 $84.68   11.573%   $94.48   $94.48   $94.50   $94.50  
  Purchase #4 $34.90   9.711%   $38.2891   $38.29   $38.30   $38.30  
  Purchase #5 $181.60   7.819%   $195.7993   $195.80   $195.80   $195.80  
  Purchase #6 $156.66   11.689%   $174.972   $174.97   $174.95   $175.00  
  Purchase #7 $191.45   13.498%   $217.2919   $217.29   $217.30   $217.30  
  7 purchase totals = $794.28       $879.3982   $879.40   $879.40   $879.40