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 $60.62   13.301%   $68.6831   $68.68   $68.70   $68.70  
  Purchase #2 $51.49   5.793%   $54.4728   $54.47   $54.45   $54.50  
  Purchase #3 $55.57   4.299%   $57.959   $57.96   $57.95   $58.00  
  Purchase #4 $92.27   9.676%   $101.198   $101.20   $101.20   $101.20  
  Purchase #5 $117.95   6.555%   $125.6816   $125.68   $125.70   $125.70  
  Purchase #6 $92.48   3.332%   $95.5614   $95.56   $95.55   $95.60  
  Purchase #7 $165.56   13.760%   $188.3411   $188.34   $188.35   $188.30  
  7 purchase totals = $635.94       $691.8970   $691.89   $691.90   $692.00