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 $86.51   6.302%   $91.9619   $91.96   $91.95   $92.00  
  Purchase #2 $124.27   6.145%   $131.9064   $131.91   $131.90   $131.90  
  Purchase #3 $244.63   11.777%   $273.4401   $273.44   $273.45   $273.40  
  Purchase #4 $194.82   9.158%   $212.6616   $212.66   $212.65   $212.70  
  Purchase #5 $210.97   10.531%   $233.1873   $233.19   $233.20   $233.20  
  Purchase #6 $71.94   6.665%   $76.7348   $76.73   $76.75   $76.70  
  Purchase #7 $190.78   4.279%   $198.9435   $198.94   $198.95   $198.90  
  7 purchase totals = $1,123.92       $1,218.8356   $1,218.83   $1,218.85   $1,218.80