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	$189.91	11.782%	$212.2852	$212.29	$212.30	$212.30
Purchase #2	$67.43	4.569%	$70.5109	$70.51	$70.50	$70.50
Purchase #3	$92.67	10.387%	$102.2956	$102.30	$102.30	$102.30
Purchase #4	$249.83	6.142%	$265.1746	$265.17	$265.15	$265.20
Purchase #5	$237.83	12.870%	$268.4387	$268.44	$268.45	$268.40
Purchase #6	$75.52	4.469%	$78.895	$78.90	$78.90	$78.90
Purchase #7	$226.28	11.672%	$252.6914	$252.69	$252.70	$252.70
7 purchase totals =	$1,139.47		$1,250.2914	$1,250.30	$1,250.30	$1,250.30