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 $54.38   5.333%   $57.2801   $57.28   $57.30   $57.30  
  Purchase #2 $249.56   5.720%   $263.8348   $263.83   $263.85   $263.80  
  Purchase #3 $65.28   3.393%   $67.495   $67.50   $67.50   $67.50  
  Purchase #4 $70.47   8.107%   $76.183   $76.18   $76.20   $76.20  
  Purchase #5 $151.26   7.512%   $162.6227   $162.62   $162.60   $162.60  
  Purchase #6 $183.52   9.360%   $200.6975   $200.70   $200.70   $200.70  
  Purchase #7 $58.66   13.740%   $66.7199   $66.72   $66.70   $66.70  
  7 purchase totals = $833.13       $894.8330   $894.83   $894.85   $894.80