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 $92.52   6.623%   $98.6476   $98.65   $98.65   $98.60  
  Purchase #2 $64.56   10.496%   $71.3362   $71.34   $71.35   $71.30  
  Purchase #3 $19.92   13.619%   $22.6329   $22.63   $22.65   $22.60  
  Purchase #4 $94.37   7.548%   $101.493   $101.49   $101.50   $101.50  
  Purchase #5 $85.38   13.236%   $96.6809   $96.68   $96.70   $96.70  
  Purchase #6 $175.59   12.380%   $197.328   $197.33   $197.35   $197.30  
  Purchase #7 $54.73   13.324%   $62.0222   $62.02   $62.00   $62.00  
  7 purchase totals = $587.07       $650.1408   $650.14   $650.20   $650.00