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 $239.54   11.696%   $267.5566   $267.56   $267.55   $267.60  
  Purchase #2 $151.79   4.776%   $159.0395   $159.04   $159.05   $159.00  
  Purchase #3 $114.94   9.296%   $125.6248   $125.62   $125.60   $125.60  
  Purchase #4 $233.53   4.160%   $243.2448   $243.24   $243.25   $243.20  
  Purchase #5 $171.76   13.162%   $194.3671   $194.37   $194.35   $194.40  
  Purchase #6 $244.95   9.563%   $268.3746   $268.37   $268.35   $268.40  
  Purchase #7 $159.25   9.349%   $174.1383   $174.14   $174.15   $174.10  
  7 purchase totals = $1,315.76       $1,432.3457   $1,432.34   $1,432.30   $1,432.30