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	$225.78	11.746%	$252.3001	$252.30	$252.30	$252.30
Purchase #2	$177.40	7.186%	$190.148	$190.15	$190.15	$190.10
Purchase #3	$221.44	6.463%	$235.7517	$235.75	$235.75	$235.80
Purchase #4	$109.73	12.629%	$123.5878	$123.59	$123.60	$123.60
Purchase #5	$122.33	7.176%	$131.1084	$131.11	$131.10	$131.10
Purchase #6	$134.58	3.428%	$139.1934	$139.19	$139.20	$139.20
Purchase #7	$119.50	7.226%	$128.1351	$128.14	$128.15	$128.10
7 purchase totals =	$1,110.76		$1,200.2245	$1,200.23	$1,200.25	$1,200.20