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	$99.48	13.113%	$112.5248	$112.52	$112.50	$112.50
Purchase #2	$176.78	3.708%	$183.335	$183.34	$183.35	$183.30
Purchase #3	$150.60	13.658%	$171.1689	$171.17	$171.15	$171.20
Purchase #4	$113.93	8.255%	$123.3349	$123.33	$123.35	$123.30
Purchase #5	$80.38	12.742%	$90.622	$90.62	$90.60	$90.60
Purchase #6	$234.84	3.543%	$243.1604	$243.16	$243.15	$243.20
Purchase #7	$145.38	5.462%	$153.3207	$153.32	$153.30	$153.30
7 purchase totals =	$1,001.39		$1,077.4667	$1,077.46	$1,077.40	$1,077.40