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 $181.26   5.390%   $191.0299   $191.03   $191.05   $191.00  
  Purchase #2 $95.99   10.361%   $105.9355   $105.94   $105.95   $105.90  
  Purchase #3 $20.90   8.250%   $22.6243   $22.62   $22.60   $22.60  
  Purchase #4 $109.93   4.362%   $114.7251   $114.73   $114.75   $114.70  
  Purchase #5 $98.47   13.719%   $111.9791   $111.98   $112.00   $112.00  
  Purchase #6 $179.60   7.832%   $193.6663   $193.67   $193.65   $193.70  
  Purchase #7 $27.82   7.812%   $29.9933   $29.99   $30.00   $30.00  
  7 purchase totals = $713.97       $769.9535   $769.96   $770.00   $769.90