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 $81.66   13.675%   $92.827   $92.83   $92.85   $92.80  
  Purchase #2 $22.91   3.854%   $23.793   $23.79   $23.80   $23.80  
  Purchase #3 $238.67   9.736%   $261.9069   $261.91   $261.90   $261.90  
  Purchase #4 $240.90   6.131%   $255.6696   $255.67   $255.65   $255.70  
  Purchase #5 $183.42   8.516%   $199.04   $199.04   $199.05   $199.00  
  Purchase #6 $103.76   7.768%   $111.8201   $111.82   $111.80   $111.80  
  Purchase #7 $123.38   7.528%   $132.668   $132.67   $132.65   $132.70  
  7 purchase totals = $994.70       $1,077.7246   $1,077.73   $1,077.70   $1,077.70