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 $127.57   5.807%   $134.978   $134.98   $135.00   $135.00  
  Purchase #2 $240.58   7.302%   $258.1472   $258.15   $258.15   $258.10  
  Purchase #3 $69.31   5.612%   $73.1997   $73.20   $73.20   $73.20  
  Purchase #4 $14.96   10.475%   $16.5271   $16.53   $16.55   $16.50  
  Purchase #5 $216.47   12.836%   $244.2561   $244.26   $244.25   $244.30  
  Purchase #6 $242.65   13.341%   $275.0219   $275.02   $275.00   $275.00  
  Purchase #7 $199.41   3.542%   $206.4731   $206.47   $206.45   $206.50  
  7 purchase totals = $1,110.95       $1,208.6031   $1,208.61   $1,208.60   $1,208.60