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 $232.35   10.485%   $256.7119   $256.71   $256.70   $256.70  
  Purchase #2 $46.37   8.465%   $50.2952   $50.30   $50.30   $50.30  
  Purchase #3 $217.35   8.113%   $234.9836   $234.98   $235.00   $235.00  
  Purchase #4 $182.91   8.221%   $197.947   $197.95   $197.95   $197.90  
  Purchase #5 $66.78   9.407%   $73.062   $73.06   $73.05   $73.10  
  Purchase #6 $116.34   6.153%   $123.4984   $123.50   $123.50   $123.50  
  Purchase #7 $211.92   12.735%   $238.908   $238.91   $238.90   $238.90  
  7 purchase totals = $1,074.02       $1,175.4061   $1,175.41   $1,175.40   $1,175.40