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	$58.40	6.333%	$62.0985	$62.10	$62.10	$62.10
Purchase #2	$105.45	11.777%	$117.8688	$117.87	$117.85	$117.90
Purchase #3	$171.51	10.187%	$188.9817	$188.98	$189.00	$189.00
Purchase #4	$165.82	3.814%	$172.1444	$172.14	$172.15	$172.10
Purchase #5	$73.94	11.607%	$82.5222	$82.52	$82.50	$82.50
Purchase #6	$171.30	8.580%	$185.9975	$186.00	$186.00	$186.00
Purchase #7	$70.75	3.791%	$73.4321	$73.43	$73.45	$73.40
7 purchase totals =	$817.17		$883.0452	$883.04	$883.05	$883.00