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 $57.76   12.785%   $65.1446   $65.14   $65.15   $65.10  
  Purchase #2 $62.37   12.464%   $70.1438   $70.14   $70.15   $70.10  
  Purchase #3 $195.49   3.456%   $202.2461   $202.25   $202.25   $202.20  
  Purchase #4 $18.28   9.765%   $20.065   $20.07   $20.05   $20.10  
  Purchase #5 $80.41   3.466%   $83.197   $83.20   $83.20   $83.20  
  Purchase #6 $79.98   5.613%   $84.4693   $84.47   $84.45   $84.50  
  Purchase #7 $218.97   8.306%   $237.1576   $237.16   $237.15   $237.20  
  7 purchase totals = $713.26       $762.4234   $762.43   $762.40   $762.40