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 $59.55   10.190%   $65.6181   $65.62   $65.60   $65.60  
  Purchase #2 $240.78   8.172%   $260.4565   $260.46   $260.45   $260.50  
  Purchase #3 $24.96   4.185%   $26.0046   $26.00   $26.00   $26.00  
  Purchase #4 $18.70   8.753%   $20.3368   $20.34   $20.35   $20.30  
  Purchase #5 $5.50   6.403%   $5.8522   $5.85   $5.85   $5.90  
  Purchase #6 $88.68   9.682%   $97.266   $97.27   $97.25   $97.30  
  Purchase #7 $232.66   8.287%   $251.9405   $251.94   $251.95   $251.90  
  7 purchase totals = $670.83       $727.4747   $727.48   $727.45   $727.50