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 $240.61   10.418%   $265.6767   $265.68   $265.70   $265.70  
  Purchase #2 $205.37   5.640%   $216.9529   $216.95   $216.95   $217.00  
  Purchase #3 $155.76   10.610%   $172.2861   $172.29   $172.30   $172.30  
  Purchase #4 $151.37   9.410%   $165.6139   $165.61   $165.60   $165.60  
  Purchase #5 $69.91   3.580%   $72.4128   $72.41   $72.40   $72.40  
  Purchase #6 $172.79   12.828%   $194.9555   $194.96   $194.95   $195.00  
  Purchase #7 $167.69   9.704%   $183.9626   $183.96   $183.95   $184.00  
  7 purchase totals = $1,163.50       $1,271.8605   $1,271.86   $1,271.85   $1,272.00