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 $204.79   7.152%   $219.4366   $219.44   $219.45   $219.40  
  Purchase #2 $92.57   5.747%   $97.89   $97.89   $97.90   $97.90  
  Purchase #3 $126.66   10.118%   $139.4755   $139.48   $139.50   $139.50  
  Purchase #4 $63.56   12.684%   $71.622   $71.62   $71.60   $71.60  
  Purchase #5 $245.49   5.491%   $258.9699   $258.97   $258.95   $259.00  
  Purchase #6 $197.57   5.515%   $208.466   $208.47   $208.45   $208.50  
  Purchase #7 $52.93   7.807%   $57.0622   $57.06   $57.05   $57.10  
  7 purchase totals = $983.57       $1,052.9222   $1,052.93   $1,052.90   $1,053.00