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 $245.85   8.630%   $267.0669   $267.07   $267.05   $267.10  
  Purchase #2 $124.95   5.620%   $131.9722   $131.97   $131.95   $132.00  
  Purchase #3 $67.41   12.740%   $75.998   $76.00   $76.00   $76.00  
  Purchase #4 $137.72   5.861%   $145.7918   $145.79   $145.80   $145.80  
  Purchase #5 $31.76   3.502%   $32.8722   $32.87   $32.85   $32.90  
  Purchase #6 $234.38   8.297%   $253.8265   $253.83   $253.85   $253.80  
  Purchase #7 $107.33   6.323%   $114.1165   $114.12   $114.10   $114.10  
  7 purchase totals = $949.40       $1,021.6441   $1,021.65   $1,021.60   $1,021.70