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	$75.92	3.201%	$78.3502	$78.35	$78.35	$78.40
Purchase #2	$80.79	10.487%	$89.2624	$89.26	$89.25	$89.30
Purchase #3	$82.49	7.274%	$88.4903	$88.49	$88.50	$88.50
Purchase #4	$102.59	3.637%	$106.3212	$106.32	$106.30	$106.30
Purchase #5	$41.35	12.276%	$46.4261	$46.43	$46.45	$46.40
Purchase #6	$148.40	8.722%	$161.3434	$161.34	$161.35	$161.30
Purchase #7	$153.27	11.658%	$171.1382	$171.14	$171.15	$171.10
7 purchase totals =	$684.81		$741.3318	$741.33	$741.35	$741.30