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	$197.89	5.772%	$209.3122	$209.31	$209.30	$209.30
Purchase #2	$129.90	12.788%	$146.5116	$146.51	$146.50	$146.50
Purchase #3	$245.28	10.540%	$271.1325	$271.13	$271.15	$271.10
Purchase #4	$89.32	12.508%	$100.4921	$100.49	$100.50	$100.50
Purchase #5	$133.43	13.729%	$151.7486	$151.75	$151.75	$151.70
Purchase #6	$173.82	4.811%	$182.1825	$182.18	$182.20	$182.20
Purchase #7	$55.30	12.758%	$62.3552	$62.36	$62.35	$62.40
7 purchase totals =	$1,024.94		$1,123.7347	$1,123.73	$1,123.75	$1,123.70