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 $241.55   5.637%   $255.1662   $255.17   $255.15   $255.20  
  Purchase #2 $53.71   3.491%   $55.585   $55.59   $55.60   $55.60  
  Purchase #3 $71.88   3.463%   $74.3692   $74.37   $74.35   $74.40  
  Purchase #4 $95.77   9.174%   $104.5559   $104.56   $104.55   $104.60  
  Purchase #5 $55.46   9.345%   $60.6427   $60.64   $60.65   $60.60  
  Purchase #6 $136.64   12.532%   $153.7637   $153.76   $153.75   $153.80  
  Purchase #7 $238.57   10.287%   $263.1117   $263.11   $263.10   $263.10  
  7 purchase totals = $893.58       $967.1944   $967.20   $967.15   $967.30