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 $110.61   12.269%   $124.1807   $124.18   $124.20   $124.20  
  Purchase #2 $151.92   4.784%   $159.1879   $159.19   $159.20   $159.20  
  Purchase #3 $183.38   9.705%   $201.177   $201.18   $201.20   $201.20  
  Purchase #4 $33.65   12.259%   $37.7752   $37.78   $37.80   $37.80  
  Purchase #5 $172.85   5.674%   $182.6575   $182.66   $182.65   $182.70  
  Purchase #6 $236.96   9.524%   $259.5281   $259.53   $259.55   $259.50  
  Purchase #7 $121.38   8.757%   $132.0092   $132.01   $132.00   $132.00  
  7 purchase totals = $1,010.75       $1,096.5156   $1,096.53   $1,096.60   $1,096.60