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 $77.48   7.762%   $83.494   $83.49   $83.50   $83.50  
  Purchase #2 $159.73   13.527%   $181.3367   $181.34   $181.35   $181.30  
  Purchase #3 $143.51   4.581%   $150.0842   $150.08   $150.10   $150.10  
  Purchase #4 $70.62   8.778%   $76.819   $76.82   $76.80   $76.80  
  Purchase #5 $124.63   6.641%   $132.9067   $132.91   $132.90   $132.90  
  Purchase #6 $214.56   10.453%   $236.988   $236.99   $237.00   $237.00  
  Purchase #7 $173.76   11.533%   $193.7997   $193.80   $193.80   $193.80  
  7 purchase totals = $964.29       $1,055.4283   $1,055.43   $1,055.45   $1,055.40