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 $238.56   3.209%   $246.2154   $246.22   $246.20   $246.20  
  Purchase #2 $65.81   8.252%   $71.2406   $71.24   $71.25   $71.20  
  Purchase #3 $121.70   8.249%   $131.739   $131.74   $131.75   $131.70  
  Purchase #4 $232.43   4.606%   $243.1357   $243.14   $243.15   $243.10  
  Purchase #5 $136.60   3.725%   $141.6884   $141.69   $141.70   $141.70  
  Purchase #6 $20.83   11.279%   $23.1794   $23.18   $23.20   $23.20  
  Purchase #7 $187.44   8.359%   $203.1081   $203.11   $203.10   $203.10  
  7 purchase totals = $1,003.37       $1,060.3066   $1,060.32   $1,060.35   $1,060.20