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 $59.69   6.519%   $63.5812   $63.58   $63.60   $63.60  
  Purchase #2 $21.32   9.407%   $23.3256   $23.33   $23.35   $23.30  
  Purchase #3 $168.77   11.383%   $187.9811   $187.98   $188.00   $188.00  
  Purchase #4 $111.55   3.580%   $115.5435   $115.54   $115.55   $115.50  
  Purchase #5 $205.61   12.571%   $231.4572   $231.46   $231.45   $231.50  
  Purchase #6 $87.68   13.790%   $99.7711   $99.77   $99.75   $99.80  
  Purchase #7 $146.89   5.496%   $154.9631   $154.96   $154.95   $155.00  
  7 purchase totals = $801.51       $876.6228   $876.62   $876.65   $876.70