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 $212.73   11.612%   $237.4322   $237.43   $237.45   $237.40  
  Purchase #2 $70.44   9.306%   $76.9951   $77.00   $77.00   $77.00  
  Purchase #3 $35.78   10.382%   $39.4947   $39.49   $39.50   $39.50  
  Purchase #4 $119.99   12.849%   $135.4075   $135.41   $135.40   $135.40  
  Purchase #5 $165.48   4.742%   $173.3271   $173.33   $173.35   $173.30  
  Purchase #6 $152.27   12.302%   $171.0023   $171.00   $171.00   $171.00  
  Purchase #7 $37.35   6.125%   $39.6377   $39.64   $39.65   $39.60  
  7 purchase totals = $794.04       $873.2966   $873.30   $873.35   $873.20