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 $56.77   5.703%   $60.0076   $60.01   $60.00   $60.00  
  Purchase #2 $181.30   13.138%   $205.1192   $205.12   $205.10   $205.10  
  Purchase #3 $34.96   12.143%   $39.2052   $39.21   $39.20   $39.20  
  Purchase #4 $115.33   7.763%   $124.2831   $124.28   $124.30   $124.30  
  Purchase #5 $217.98   6.204%   $231.5035   $231.50   $231.50   $231.50  
  Purchase #6 $46.33   5.196%   $48.7373   $48.74   $48.75   $48.70  
  Purchase #7 $219.31   13.710%   $249.3774   $249.38   $249.40   $249.40  
  7 purchase totals = $871.98       $958.2333   $958.24   $958.25   $958.20