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	$230.82	5.587%	$243.7159	$243.72	$243.70	$243.70
Purchase #2	$116.50	5.738%	$123.1848	$123.18	$123.20	$123.20
Purchase #3	$199.88	11.640%	$223.146	$223.15	$223.15	$223.10
Purchase #4	$141.56	7.496%	$152.1713	$152.17	$152.15	$152.20
Purchase #5	$178.61	11.408%	$198.9858	$198.99	$199.00	$199.00
Purchase #6	$131.63	12.560%	$148.1627	$148.16	$148.15	$148.20
Purchase #7	$233.63	7.124%	$250.2738	$250.27	$250.25	$250.30
7 purchase totals =	$1,232.63		$1,339.6403	$1,339.64	$1,339.60	$1,339.70