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 $241.65   8.853%   $263.0433   $263.04   $263.05   $263.00  
  Purchase #2 $139.29   3.269%   $143.8434   $143.84   $143.85   $143.80  
  Purchase #3 $13.76   6.195%   $14.6124   $14.61   $14.60   $14.60  
  Purchase #4 $90.86   11.760%   $101.5451   $101.55   $101.55   $101.50  
  Purchase #5 $68.78   10.420%   $75.9469   $75.95   $75.95   $75.90  
  Purchase #6 $228.87   12.157%   $256.6937   $256.69   $256.70   $256.70  
  Purchase #7 $236.29   6.307%   $251.1928   $251.19   $251.20   $251.20  
  7 purchase totals = $1,019.50       $1,106.8776   $1,106.87   $1,106.90   $1,106.70