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 $97.72   3.602%   $101.2399   $101.24   $101.25   $101.20  
  Purchase #2 $95.97   7.188%   $102.8683   $102.87   $102.85   $102.90  
  Purchase #3 $56.86   8.414%   $61.6442   $61.64   $61.65   $61.60  
  Purchase #4 $48.45   12.863%   $54.6821   $54.68   $54.70   $54.70  
  Purchase #5 $213.97   12.274%   $240.2327   $240.23   $240.25   $240.20  
  Purchase #6 $95.75   7.601%   $103.028   $103.03   $103.05   $103.00  
  Purchase #7 $84.72   13.725%   $96.3478   $96.35   $96.35   $96.30  
  7 purchase totals = $693.44       $760.0430   $760.04   $760.10   $759.90