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 $115.85   7.255%   $124.2549   $124.25   $124.25   $124.30  
  Purchase #2 $136.78   9.151%   $149.2967   $149.30   $149.30   $149.30  
  Purchase #3 $85.81   12.604%   $96.6255   $96.63   $96.65   $96.60  
  Purchase #4 $213.56   9.390%   $233.6133   $233.61   $233.60   $233.60  
  Purchase #5 $94.75   10.540%   $104.7367   $104.74   $104.75   $104.70  
  Purchase #6 $58.62   5.748%   $61.9895   $61.99   $62.00   $62.00  
  Purchase #7 $191.40   7.367%   $205.5004   $205.50   $205.50   $205.50  
  7 purchase totals = $896.77       $976.0170   $976.02   $976.05   $976.00