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 $67.53   12.469%   $75.9503   $75.95   $75.95   $76.00  
  Purchase #2 $184.72   11.761%   $206.4449   $206.44   $206.45   $206.40  
  Purchase #3 $159.38   3.783%   $165.4093   $165.41   $165.40   $165.40  
  Purchase #4 $6.61   4.406%   $6.9012   $6.90   $6.90   $6.90  
  Purchase #5 $126.48   6.343%   $134.5026   $134.50   $134.50   $134.50  
  Purchase #6 $117.43   6.596%   $125.1757   $125.18   $125.20   $125.20  
  Purchase #7 $241.82   13.133%   $273.5782   $273.58   $273.60   $273.60  
  7 purchase totals = $903.97       $987.9622   $987.96   $988.00   $988.00