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	$244.81	11.695%	$273.4405	$273.44	$273.45	$273.40
Purchase #2	$90.28	11.122%	$100.3209	$100.32	$100.30	$100.30
Purchase #3	$223.25	4.546%	$233.3989	$233.40	$233.40	$233.40
Purchase #4	$165.32	12.687%	$186.2941	$186.29	$186.30	$186.30
Purchase #5	$101.76	9.221%	$111.1433	$111.14	$111.15	$111.10
Purchase #6	$124.49	3.346%	$128.6554	$128.66	$128.65	$128.70
Purchase #7	$64.58	13.375%	$73.2176	$73.22	$73.20	$73.20
7 purchase totals =	$1,014.49		$1,106.4707	$1,106.47	$1,106.45	$1,106.40