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	$178.33	12.463%	$200.5553	$200.56	$200.55	$200.60
Purchase #2	$185.29	13.481%	$210.2689	$210.27	$210.25	$210.30
Purchase #3	$80.46	6.744%	$85.8862	$85.89	$85.90	$85.90
Purchase #4	$23.57	5.484%	$24.8626	$24.86	$24.85	$24.90
Purchase #5	$165.54	4.808%	$173.4992	$173.50	$173.50	$173.50
Purchase #6	$78.90	8.473%	$85.5852	$85.59	$85.60	$85.60
Purchase #7	$12.32	8.541%	$13.3723	$13.37	$13.35	$13.40
7 purchase totals =	$724.41		$794.0297	$794.04	$794.00	$794.20