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 $196.94   5.431%   $207.6358   $207.64   $207.65   $207.60  
  Purchase #2 $55.34   3.544%   $57.3012   $57.30   $57.30   $57.30  
  Purchase #3 $101.83   11.774%   $113.8195   $113.82   $113.80   $113.80  
  Purchase #4 $167.55   12.385%   $188.3011   $188.30   $188.30   $188.30  
  Purchase #5 $119.49   5.218%   $125.725   $125.73   $125.75   $125.70  
  Purchase #6 $100.89   13.715%   $114.7271   $114.73   $114.75   $114.70  
  Purchase #7 $33.89   7.594%   $36.4636   $36.46   $36.45   $36.50  
  7 purchase totals = $775.93       $843.9733   $843.98   $844.00   $843.90