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 $57.51   4.264%   $59.9622   $59.96   $59.95   $60.00  
  Purchase #2 $151.60   8.380%   $164.3041   $164.30   $164.30   $164.30  
  Purchase #3 $71.68   13.592%   $81.4227   $81.42   $81.40   $81.40  
  Purchase #4 $247.87   11.422%   $276.1817   $276.18   $276.20   $276.20  
  Purchase #5 $75.33   10.450%   $83.202   $83.20   $83.20   $83.20  
  Purchase #6 $131.82   11.225%   $146.6168   $146.62   $146.60   $146.60  
  Purchase #7 $229.25   3.210%   $236.6089   $236.61   $236.60   $236.60  
  7 purchase totals = $965.06       $1,048.2984   $1,048.29   $1,048.25   $1,048.30