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	$250.80	5.521%	$264.6467	$264.65	$264.65	$264.60
Purchase #2	$59.56	9.160%	$65.0157	$65.02	$65.00	$65.00
Purchase #3	$97.32	12.179%	$109.1726	$109.17	$109.15	$109.20
Purchase #4	$217.28	13.711%	$247.0713	$247.07	$247.05	$247.10
Purchase #5	$176.87	10.290%	$195.0699	$195.07	$195.05	$195.10
Purchase #6	$210.60	9.796%	$231.2304	$231.23	$231.25	$231.20
Purchase #7	$128.60	11.241%	$143.0559	$143.06	$143.05	$143.10
7 purchase totals =	$1,141.03		$1,255.2625	$1,255.27	$1,255.20	$1,255.30