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 $136.38   11.840%   $152.5274   $152.53   $152.55   $152.50  
  Purchase #2 $164.41   9.873%   $180.6422   $180.64   $180.65   $180.60  
  Purchase #3 $241.93   12.784%   $272.8583   $272.86   $272.85   $272.90  
  Purchase #4 $113.89   6.522%   $121.3179   $121.32   $121.30   $121.30  
  Purchase #5 $215.53   13.781%   $245.2322   $245.23   $245.25   $245.20  
  Purchase #6 $44.84   10.449%   $49.5253   $49.53   $49.55   $49.50  
  Purchase #7 $229.81   4.302%   $239.6964   $239.70   $239.70   $239.70  
  7 purchase totals = $1,146.79       $1,261.7997   $1,261.81   $1,261.85   $1,261.70