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 $32.76   4.406%   $34.2034   $34.20   $34.20   $34.20  
  Purchase #2 $182.41   10.338%   $201.2675   $201.27   $201.25   $201.30  
  Purchase #3 $107.50   11.786%   $120.17   $120.17   $120.15   $120.20  
  Purchase #4 $117.54   12.415%   $132.1326   $132.13   $132.15   $132.10  
  Purchase #5 $76.34   9.761%   $83.7915   $83.79   $83.80   $83.80  
  Purchase #6 $101.26   4.158%   $105.4704   $105.47   $105.45   $105.50  
  Purchase #7 $111.86   6.776%   $119.4396   $119.44   $119.45   $119.40  
  7 purchase totals = $729.67       $796.4750   $796.47   $796.45   $796.50