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 $32.35   6.739%   $34.5301   $34.53   $34.55   $34.50  
  Purchase #2 $61.42   4.510%   $64.19   $64.19   $64.20   $64.20  
  Purchase #3 $58.64   8.832%   $63.8191   $63.82   $63.80   $63.80  
  Purchase #4 $88.75   5.204%   $93.3686   $93.37   $93.35   $93.40  
  Purchase #5 $192.74   4.836%   $202.0609   $202.06   $202.05   $202.10  
  Purchase #6 $157.63   4.281%   $164.3781   $164.38   $164.40   $164.40  
  Purchase #7 $164.92   7.304%   $176.9658   $176.97   $176.95   $177.00  
  7 purchase totals = $756.45       $799.3126   $799.32   $799.30   $799.40