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	$246.29	3.671%	$255.3313	$255.33	$255.35	$255.30
Purchase #2	$162.87	9.845%	$178.9046	$178.90	$178.90	$178.90
Purchase #3	$139.54	9.286%	$152.4977	$152.50	$152.50	$152.50
Purchase #4	$195.72	4.497%	$204.5215	$204.52	$204.50	$204.50
Purchase #5	$150.87	4.279%	$157.3257	$157.33	$157.35	$157.30
Purchase #6	$88.51	12.714%	$99.7632	$99.76	$99.75	$99.80
Purchase #7	$7.92	12.719%	$8.9273	$8.93	$8.95	$8.90
7 purchase totals =	$991.72		$1,057.2713	$1,057.27	$1,057.30	$1,057.20