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	$151.98	13.156%	$171.9745	$171.97	$171.95	$172.00
Purchase #2	$125.71	12.373%	$141.2641	$141.26	$141.25	$141.30
Purchase #3	$97.76	13.847%	$111.2968	$111.30	$111.30	$111.30
Purchase #4	$58.36	12.869%	$65.8703	$65.87	$65.85	$65.90
Purchase #5	$43.74	5.569%	$46.1759	$46.18	$46.20	$46.20
Purchase #6	$82.47	8.453%	$89.4412	$89.44	$89.45	$89.40
Purchase #7	$247.78	13.615%	$281.5152	$281.52	$281.50	$281.50
7 purchase totals =	$807.80		$907.5380	$907.54	$907.50	$907.60