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 $118.65   12.388%   $133.3484   $133.35   $133.35   $133.30  
  Purchase #2 $219.93   11.662%   $245.5782   $245.58   $245.60   $245.60  
  Purchase #3 $115.53   3.799%   $119.919   $119.92   $119.90   $119.90  
  Purchase #4 $82.31   13.861%   $93.719   $93.72   $93.70   $93.70  
  Purchase #5 $169.99   10.616%   $188.0361   $188.04   $188.05   $188.00  
  Purchase #6 $176.32   12.271%   $197.9562   $197.96   $197.95   $198.00  
  Purchase #7 $140.38   4.462%   $146.6438   $146.64   $146.65   $146.60  
  7 purchase totals = $1,023.11       $1,125.2007   $1,125.21   $1,125.20   $1,125.10