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 $241.81   7.117%   $259.0196   $259.02   $259.00   $259.00  
  Purchase #2 $150.29   6.295%   $159.7508   $159.75   $159.75   $159.80  
  Purchase #3 $191.25   12.464%   $215.0874   $215.09   $215.10   $215.10  
  Purchase #4 $239.47   3.823%   $248.6249   $248.62   $248.60   $248.60  
  Purchase #5 $62.93   7.636%   $67.7353   $67.74   $67.75   $67.70  
  Purchase #6 $149.72   4.408%   $156.3197   $156.32   $156.30   $156.30  
  Purchase #7 $230.42   13.396%   $261.2871   $261.29   $261.30   $261.30  
  7 purchase totals = $1,265.89       $1,367.8248   $1,367.83   $1,367.80   $1,367.80