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	$16.88	7.160%	$18.0886	$18.09	$18.10	$18.10
Purchase #2	$29.42	9.158%	$32.1143	$32.11	$32.10	$32.10
Purchase #3	$65.90	12.642%	$74.2311	$74.23	$74.25	$74.20
Purchase #4	$209.30	10.400%	$231.0672	$231.07	$231.05	$231.10
Purchase #5	$85.72	7.483%	$92.1344	$92.13	$92.15	$92.10
Purchase #6	$83.73	8.386%	$90.7516	$90.75	$90.75	$90.80
Purchase #7	$164.99	12.690%	$185.9272	$185.93	$185.95	$185.90
7 purchase totals =	$655.94		$724.3144	$724.31	$724.35	$724.30