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 $209.31   13.832%   $238.2618   $238.26   $238.25   $238.30  
  Purchase #2 $125.34   8.778%   $136.3423   $136.34   $136.35   $136.30  
  Purchase #3 $103.47   11.758%   $115.636   $115.64   $115.65   $115.60  
  Purchase #4 $172.57   4.152%   $179.7351   $179.74   $179.75   $179.70  
  Purchase #5 $52.73   9.668%   $57.8279   $57.83   $57.85   $57.80  
  Purchase #6 $104.85   13.215%   $118.7059   $118.71   $118.70   $118.70  
  Purchase #7 $177.27   6.390%   $188.5976   $188.60   $188.60   $188.60  
  7 purchase totals = $945.54       $1,035.1066   $1,035.12   $1,035.15   $1,035.00