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 $226.31   4.276%   $235.987   $235.99   $236.00   $236.00  
  Purchase #2 $87.44   11.828%   $97.7824   $97.78   $97.80   $97.80  
  Purchase #3 $62.42   4.439%   $65.1908   $65.19   $65.20   $65.20  
  Purchase #4 $163.46   13.242%   $185.1054   $185.11   $185.10   $185.10  
  Purchase #5 $133.41   9.322%   $145.8465   $145.85   $145.85   $145.80  
  Purchase #6 $226.70   13.188%   $256.5972   $256.60   $256.60   $256.60  
  Purchase #7 $167.39   6.120%   $177.6343   $177.63   $177.65   $177.60  
  7 purchase totals = $1,067.13       $1,164.1436   $1,164.15   $1,164.20   $1,164.10