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 $51.46   5.252%   $54.1627   $54.16   $54.15   $54.20  
  Purchase #2 $41.79   6.339%   $44.4391   $44.44   $44.45   $44.40  
  Purchase #3 $95.40   7.218%   $102.286   $102.29   $102.30   $102.30  
  Purchase #4 $15.75   7.361%   $16.9094   $16.91   $16.90   $16.90  
  Purchase #5 $154.27   6.348%   $164.0631   $164.06   $164.05   $164.10  
  Purchase #6 $187.76   9.103%   $204.8518   $204.85   $204.85   $204.90  
  Purchase #7 $135.41   10.194%   $149.2137   $149.21   $149.20   $149.20  
  7 purchase totals = $681.84       $735.9258   $735.92   $735.90   $736.00