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 $22.92   6.310%   $24.3663   $24.37   $24.35   $24.40  
  Purchase #2 $250.80   9.808%   $275.3985   $275.40   $275.40   $275.40  
  Purchase #3 $171.52   6.539%   $182.7357   $182.74   $182.75   $182.70  
  Purchase #4 $61.49   6.310%   $65.37   $65.37   $65.35   $65.40  
  Purchase #5 $35.76   7.153%   $38.3179   $38.32   $38.30   $38.30  
  Purchase #6 $116.83   3.491%   $120.9085   $120.91   $120.90   $120.90  
  Purchase #7 $61.60   6.163%   $65.3964   $65.40   $65.40   $65.40  
  7 purchase totals = $720.92       $772.4933   $772.51   $772.45   $772.50