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	$27.50	6.287%	$29.2289	$29.23	$29.25	$29.20
Purchase #2	$165.74	12.433%	$186.3465	$186.35	$186.35	$186.30
Purchase #3	$202.96	12.721%	$228.7785	$228.78	$228.80	$228.80
Purchase #4	$74.69	3.778%	$77.5118	$77.51	$77.50	$77.50
Purchase #5	$74.56	10.256%	$82.2069	$82.21	$82.20	$82.20
Purchase #6	$169.40	12.581%	$190.7122	$190.71	$190.70	$190.70
Purchase #7	$113.92	11.731%	$127.284	$127.28	$127.30	$127.30
7 purchase totals =	$828.77		$922.0688	$922.07	$922.10	$922.00