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 $35.59   6.748%   $37.9916   $37.99   $38.00   $38.00  
  Purchase #2 $236.68   7.327%   $254.0215   $254.02   $254.00   $254.00  
  Purchase #3 $213.76   13.742%   $243.1349   $243.13   $243.15   $243.10  
  Purchase #4 $125.72   7.567%   $135.2332   $135.23   $135.25   $135.20  
  Purchase #5 $62.63   6.267%   $66.555   $66.56   $66.55   $66.60  
  Purchase #6 $167.67   9.648%   $183.8468   $183.85   $183.85   $183.80  
  Purchase #7 $250.89   13.724%   $285.3221   $285.32   $285.30   $285.30  
  7 purchase totals = $1,092.94       $1,206.1051   $1,206.10   $1,206.10   $1,206.00