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 $5.40   11.173%   $6.0033   $6.00   $6.00   $6.00  
  Purchase #2 $62.97   12.774%   $71.0138   $71.01   $71.00   $71.00  
  Purchase #3 $214.78   4.472%   $224.385   $224.39   $224.40   $224.40  
  Purchase #4 $74.48   10.196%   $82.074   $82.07   $82.05   $82.10  
  Purchase #5 $61.78   5.502%   $65.1791   $65.18   $65.20   $65.20  
  Purchase #6 $226.46   7.721%   $243.945   $243.95   $243.95   $243.90  
  Purchase #7 $51.56   11.638%   $57.5606   $57.56   $57.55   $57.60  
  7 purchase totals = $697.43       $750.1608   $750.16   $750.15   $750.20