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 $219.33   13.848%   $249.7028   $249.70   $249.70   $249.70  
  Purchase #2 $46.89   5.857%   $49.6363   $49.64   $49.65   $49.60  
  Purchase #3 $41.86   8.213%   $45.298   $45.30   $45.30   $45.30  
  Purchase #4 $164.28   11.454%   $183.0966   $183.10   $183.10   $183.10  
  Purchase #5 $194.94   9.585%   $213.625   $213.63   $213.65   $213.60  
  Purchase #6 $82.32   12.353%   $92.489   $92.49   $92.50   $92.50  
  Purchase #7 $31.65   12.340%   $35.5556   $35.56   $35.55   $35.60  
  7 purchase totals = $781.27       $869.4033   $869.42   $869.45   $869.40