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 $58.69   8.271%   $63.5442   $63.54   $63.55   $63.50  
  Purchase #2 $63.65   12.111%   $71.3587   $71.36   $71.35   $71.40  
  Purchase #3 $71.83   10.206%   $79.161   $79.16   $79.15   $79.20  
  Purchase #4 $40.67   8.702%   $44.2091   $44.21   $44.20   $44.20  
  Purchase #5 $58.72   9.283%   $64.171   $64.17   $64.15   $64.20  
  Purchase #6 $200.82   10.477%   $221.8599   $221.86   $221.85   $221.90  
  Purchase #7 $162.99   8.401%   $176.6828   $176.68   $176.70   $176.70  
  7 purchase totals = $657.37       $720.9867   $720.98   $720.95   $721.10