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	$181.49	4.411%	$189.4955	$189.50	$189.50	$189.50
Purchase #2	$231.71	8.705%	$251.8804	$251.88	$251.90	$251.90
Purchase #3	$246.56	11.718%	$275.4519	$275.45	$275.45	$275.50
Purchase #4	$244.45	4.490%	$255.4258	$255.43	$255.45	$255.40
Purchase #5	$243.76	11.562%	$271.9435	$271.94	$271.95	$271.90
Purchase #6	$103.47	5.844%	$109.5168	$109.52	$109.50	$109.50
Purchase #7	$23.67	5.802%	$25.0433	$25.04	$25.05	$25.00
7 purchase totals =	$1,275.11		$1,378.7572	$1,378.76	$1,378.80	$1,378.70