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 $134.82   8.502%   $146.2824   $146.28   $146.30   $146.30  
  Purchase #2 $124.89   10.271%   $137.7175   $137.72   $137.70   $137.70  
  Purchase #3 $87.36   4.508%   $91.2982   $91.30   $91.30   $91.30  
  Purchase #4 $197.36   7.423%   $212.01   $212.01   $212.00   $212.00  
  Purchase #5 $107.69   5.334%   $113.4342   $113.43   $113.45   $113.40  
  Purchase #6 $234.62   12.142%   $263.1076   $263.11   $263.10   $263.10  
  Purchase #7 $66.64   4.733%   $69.7941   $69.79   $69.80   $69.80  
  7 purchase totals = $953.38       $1,033.6440   $1,033.64   $1,033.65   $1,033.60