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 $231.34   13.695%   $263.022   $263.02   $263.00   $263.00  
  Purchase #2 $129.76   4.520%   $135.6252   $135.63   $135.65   $135.60  
  Purchase #3 $57.34   9.116%   $62.5671   $62.57   $62.55   $62.60  
  Purchase #4 $101.39   3.119%   $104.5524   $104.55   $104.55   $104.60  
  Purchase #5 $48.89   10.181%   $53.8675   $53.87   $53.85   $53.90  
  Purchase #6 $25.44   8.560%   $27.6177   $27.62   $27.60   $27.60  
  Purchase #7 $34.32   4.673%   $35.9238   $35.92   $35.90   $35.90  
  7 purchase totals = $628.48       $683.1757   $683.18   $683.10   $683.20