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 $55.76   9.757%   $61.2005   $61.20   $61.20   $61.20  
  Purchase #2 $167.49   4.749%   $175.4441   $175.44   $175.45   $175.40  
  Purchase #3 $156.48   6.343%   $166.4055   $166.41   $166.40   $166.40  
  Purchase #4 $158.76   6.581%   $169.208   $169.21   $169.20   $169.20  
  Purchase #5 $124.50   9.480%   $136.3026   $136.30   $136.30   $136.30  
  Purchase #6 $206.45   6.702%   $220.2863   $220.29   $220.30   $220.30  
  Purchase #7 $118.33   10.243%   $130.4505   $130.45   $130.45   $130.50  
  7 purchase totals = $987.77       $1,059.2975   $1,059.30   $1,059.30   $1,059.30