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 $14.67   12.658%   $16.5269   $16.53   $16.55   $16.50  
  Purchase #2 $59.66   9.384%   $65.2585   $65.26   $65.25   $65.30  
  Purchase #3 $22.53   8.403%   $24.4232   $24.42   $24.40   $24.40  
  Purchase #4 $52.51   9.732%   $57.6203   $57.62   $57.60   $57.60  
  Purchase #5 $139.63   6.567%   $148.7995   $148.80   $148.80   $148.80  
  Purchase #6 $83.52   10.648%   $92.4132   $92.41   $92.40   $92.40  
  Purchase #7 $83.67   13.553%   $95.0098   $95.01   $95.00   $95.00  
  7 purchase totals = $456.19       $500.0514   $500.05   $500.00   $500.00