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 $244.78   6.314%   $260.2354   $260.24   $260.25   $260.20  
  Purchase #2 $55.39   4.148%   $57.6876   $57.69   $57.70   $57.70  
  Purchase #3 $162.29   12.683%   $182.8732   $182.87   $182.85   $182.90  
  Purchase #4 $45.62   13.104%   $51.598   $51.60   $51.60   $51.60  
  Purchase #5 $123.47   5.467%   $130.2201   $130.22   $130.20   $130.20  
  Purchase #6 $194.63   3.247%   $200.9496   $200.95   $200.95   $200.90  
  Purchase #7 $228.46   6.642%   $243.6343   $243.63   $243.65   $243.60  
  7 purchase totals = $1,054.64       $1,127.1982   $1,127.20   $1,127.20   $1,127.10