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	$46.45	5.265%	$48.8956	$48.90	$48.90	$48.90
Purchase #2	$82.98	7.168%	$88.928	$88.93	$88.95	$88.90
Purchase #3	$172.33	3.369%	$178.1358	$178.14	$178.15	$178.10
Purchase #4	$176.78	13.254%	$200.2104	$200.21	$200.20	$200.20
Purchase #5	$152.92	11.638%	$170.7168	$170.72	$170.70	$170.70
Purchase #6	$159.88	10.146%	$176.1014	$176.10	$176.10	$176.10
Purchase #7	$54.40	9.603%	$59.624	$59.62	$59.60	$59.60
7 purchase totals =	$845.74		$922.6120	$922.62	$922.60	$922.50