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	$224.57	13.262%	$254.3525	$254.35	$254.35	$254.40
Purchase #2	$109.82	12.718%	$123.7869	$123.79	$123.80	$123.80
Purchase #3	$218.26	5.363%	$229.9653	$229.97	$229.95	$230.00
Purchase #4	$86.83	5.328%	$91.4563	$91.46	$91.45	$91.50
Purchase #5	$172.95	5.518%	$182.4934	$182.49	$182.50	$182.50
Purchase #6	$132.92	6.268%	$141.2514	$141.25	$141.25	$141.30
Purchase #7	$135.41	6.432%	$144.1196	$144.12	$144.10	$144.10
7 purchase totals =	$1,080.76		$1,167.4254	$1,167.43	$1,167.40	$1,167.60