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	$121.40	9.325%	$132.7206	$132.72	$132.70	$132.70
Purchase #2	$115.45	4.330%	$120.449	$120.45	$120.45	$120.40
Purchase #3	$11.83	12.693%	$13.3316	$13.33	$13.35	$13.30
Purchase #4	$68.77	6.721%	$73.392	$73.39	$73.40	$73.40
Purchase #5	$165.94	4.538%	$173.4704	$173.47	$173.45	$173.50
Purchase #6	$54.89	12.514%	$61.7589	$61.76	$61.75	$61.80
Purchase #7	$88.72	3.676%	$91.9813	$91.98	$92.00	$92.00
7 purchase totals =	$627.00		$667.1038	$667.10	$667.10	$667.10