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 $44.73   4.470%   $46.7294   $46.73   $46.75   $46.70  
  Purchase #2 $14.97   12.266%   $16.8062   $16.81   $16.80   $16.80  
  Purchase #3 $35.32   8.298%   $38.2509   $38.25   $38.25   $38.30  
  Purchase #4 $67.91   6.299%   $72.1877   $72.19   $72.20   $72.20  
  Purchase #5 $103.74   4.110%   $108.0037   $108.00   $108.00   $108.00  
  Purchase #6 $102.66   10.795%   $113.7421   $113.74   $113.75   $113.70  
  Purchase #7 $68.93   8.129%   $74.5333   $74.53   $74.55   $74.50  
  7 purchase totals = $438.26       $470.2533   $470.25   $470.30   $470.20