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 $58.67   5.654%   $61.9872   $61.99   $62.00   $62.00  
  Purchase #2 $119.86   13.443%   $135.9728   $135.97   $135.95   $136.00  
  Purchase #3 $244.69   9.638%   $268.2732   $268.27   $268.25   $268.30  
  Purchase #4 $68.74   9.852%   $75.5123   $75.51   $75.50   $75.50  
  Purchase #5 $165.92   9.794%   $182.1702   $182.17   $182.15   $182.20  
  Purchase #6 $165.38   9.242%   $180.6644   $180.66   $180.65   $180.70  
  Purchase #7 $90.73   4.867%   $95.1458   $95.15   $95.15   $95.10  
  7 purchase totals = $913.99       $999.7259   $999.72   $999.65   $999.80