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 $117.97   12.754%   $133.0159   $133.02   $133.00   $133.00  
  Purchase #2 $32.61   7.184%   $34.9527   $34.95   $34.95   $35.00  
  Purchase #3 $34.86   5.316%   $36.7132   $36.71   $36.70   $36.70  
  Purchase #4 $193.36   11.454%   $215.5075   $215.51   $215.50   $215.50  
  Purchase #5 $250.58   9.837%   $275.2296   $275.23   $275.25   $275.20  
  Purchase #6 $122.48   9.845%   $134.5382   $134.54   $134.55   $134.50  
  Purchase #7 $222.31   8.265%   $240.6839   $240.68   $240.70   $240.70  
  7 purchase totals = $974.17       $1,070.6410   $1,070.64   $1,070.65   $1,070.60