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 $182.71   13.695%   $207.7321   $207.73   $207.75   $207.70  
  Purchase #2 $53.67   8.596%   $58.2835   $58.28   $58.30   $58.30  
  Purchase #3 $70.64   7.560%   $75.9804   $75.98   $76.00   $76.00  
  Purchase #4 $53.39   5.859%   $56.5181   $56.52   $56.50   $56.50  
  Purchase #5 $63.83   6.522%   $67.993   $67.99   $68.00   $68.00  
  Purchase #6 $71.31   7.402%   $76.5884   $76.59   $76.60   $76.60  
  Purchase #7 $250.31   9.541%   $274.1921   $274.19   $274.20   $274.20  
  7 purchase totals = $745.86       $817.2876   $817.28   $817.35   $817.30