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	$45.71	5.873%	$48.3945	$48.39	$48.40	$48.40
Purchase #2	$229.34	10.418%	$253.2326	$253.23	$253.25	$253.20
Purchase #3	$38.43	12.585%	$43.2664	$43.27	$43.25	$43.30
Purchase #4	$88.95	11.381%	$99.0734	$99.07	$99.05	$99.10
Purchase #5	$202.46	10.236%	$223.1838	$223.18	$223.20	$223.20
Purchase #6	$5.28	5.700%	$5.581	$5.58	$5.60	$5.60
Purchase #7	$134.38	10.683%	$148.7358	$148.74	$148.75	$148.70
7 purchase totals =	$744.55		$821.4675	$821.46	$821.50	$821.50