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	$131.86	12.275%	$148.0458	$148.05	$148.05	$148.00
Purchase #2	$180.95	13.106%	$204.6653	$204.67	$204.65	$204.70
Purchase #3	$144.38	10.836%	$160.025	$160.03	$160.05	$160.00
Purchase #4	$197.42	13.126%	$223.3333	$223.33	$223.35	$223.30
Purchase #5	$59.55	11.608%	$66.4626	$66.46	$66.45	$66.50
Purchase #6	$18.87	7.400%	$20.2664	$20.27	$20.25	$20.30
Purchase #7	$34.34	6.332%	$36.5144	$36.51	$36.50	$36.50
7 purchase totals =	$767.37		$859.3128	$859.32	$859.30	$859.30