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 $241.61   8.684%   $262.5914   $262.59   $262.60   $262.60  
  Purchase #2 $208.49   9.259%   $227.7941   $227.79   $227.80   $227.80  
  Purchase #3 $141.26   9.732%   $155.0074   $155.01   $155.00   $155.00  
  Purchase #4 $124.38   6.675%   $132.6824   $132.68   $132.70   $132.70  
  Purchase #5 $86.33   8.662%   $93.8079   $93.81   $93.80   $93.80  
  Purchase #6 $45.95   13.809%   $52.2952   $52.30   $52.30   $52.30  
  Purchase #7 $219.74   11.188%   $244.3245   $244.32   $244.30   $244.30  
  7 purchase totals = $1,067.76       $1,168.5029   $1,168.50   $1,168.50   $1,168.50