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 $84.49   13.601%   $95.9815   $95.98   $96.00   $96.00  
  Purchase #2 $52.84   10.406%   $58.3385   $58.34   $58.35   $58.30  
  Purchase #3 $9.38   12.188%   $10.5232   $10.52   $10.50   $10.50  
  Purchase #4 $21.32   11.278%   $23.7245   $23.72   $23.70   $23.70  
  Purchase #5 $228.58   7.377%   $245.4423   $245.44   $245.45   $245.40  
  Purchase #6 $82.78   12.143%   $92.832   $92.83   $92.85   $92.80  
  Purchase #7 $175.39   10.156%   $193.2026   $193.20   $193.20   $193.20  
  7 purchase totals = $654.78       $720.0446   $720.03   $720.05   $719.90