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 $85.54   7.467%   $91.9273   $91.93   $91.95   $91.90  
  Purchase #2 $13.90   13.195%   $15.7341   $15.73   $15.75   $15.70  
  Purchase #3 $177.56   8.407%   $192.4875   $192.49   $192.50   $192.50  
  Purchase #4 $50.71   11.296%   $56.4382   $56.44   $56.45   $56.40  
  Purchase #5 $206.72   7.760%   $222.7615   $222.76   $222.75   $222.80  
  Purchase #6 $75.26   7.306%   $80.7585   $80.76   $80.75   $80.80  
  Purchase #7 $116.45   6.359%   $123.8551   $123.86   $123.85   $123.90  
  7 purchase totals = $726.14       $783.9622   $783.97   $784.00   $784.00