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 $212.37   12.639%   $239.2114   $239.21   $239.20   $239.20  
  Purchase #2 $60.53   8.390%   $65.6085   $65.61   $65.60   $65.60  
  Purchase #3 $111.63   7.291%   $119.7689   $119.77   $119.75   $119.80  
  Purchase #4 $161.26   7.489%   $173.3368   $173.34   $173.35   $173.30  
  Purchase #5 $136.56   9.255%   $149.1986   $149.20   $149.20   $149.20  
  Purchase #6 $55.97   7.405%   $60.1146   $60.11   $60.10   $60.10  
  Purchase #7 $26.28   5.845%   $27.8161   $27.82   $27.80   $27.80  
  7 purchase totals = $764.60       $835.0549   $835.06   $835.00   $835.00