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 $98.38   12.412%   $110.5909   $110.59   $110.60   $110.60  
  Purchase #2 $16.48   9.306%   $18.0136   $18.01   $18.00   $18.00  
  Purchase #3 $84.26   9.600%   $92.349   $92.35   $92.35   $92.30  
  Purchase #4 $110.91   3.376%   $114.6543   $114.65   $114.65   $114.70  
  Purchase #5 $193.80   9.490%   $212.1916   $212.19   $212.20   $212.20  
  Purchase #6 $158.62   7.765%   $170.9368   $170.94   $170.95   $170.90  
  Purchase #7 $71.27   5.563%   $75.2348   $75.23   $75.25   $75.20  
  7 purchase totals = $733.72       $793.9710   $793.96   $794.00   $793.90