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 $114.55   4.211%   $119.3737   $119.37   $119.35   $119.40  
  Purchase #2 $97.68   5.198%   $102.7574   $102.76   $102.75   $102.80  
  Purchase #3 $132.95   4.621%   $139.0936   $139.09   $139.10   $139.10  
  Purchase #4 $221.30   6.715%   $236.1603   $236.16   $236.15   $236.20  
  Purchase #5 $196.90   6.349%   $209.4012   $209.40   $209.40   $209.40  
  Purchase #6 $167.92   9.183%   $183.3401   $183.34   $183.35   $183.30  
  Purchase #7 $109.89   7.870%   $118.5383   $118.54   $118.55   $118.50  
  7 purchase totals = $1,041.19       $1,108.6646   $1,108.66   $1,108.65   $1,108.70