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	$240.72	5.860%	$254.8262	$254.83	$254.85	$254.80
Purchase #2	$227.56	12.226%	$255.3815	$255.38	$255.40	$255.40
Purchase #3	$172.30	11.694%	$192.4488	$192.45	$192.45	$192.40
Purchase #4	$95.58	3.671%	$99.0887	$99.09	$99.10	$99.10
Purchase #5	$59.49	12.689%	$67.0387	$67.04	$67.05	$67.00
Purchase #6	$141.52	8.132%	$153.0284	$153.03	$153.05	$153.00
Purchase #7	$202.84	3.259%	$209.4506	$209.45	$209.45	$209.50
7 purchase totals =	$1,140.01		$1,231.2629	$1,231.27	$1,231.35	$1,231.20