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	$115.27	13.776%	$131.1496	$131.15	$131.15	$131.10
Purchase #2	$51.98	7.541%	$55.8998	$55.90	$55.90	$55.90
Purchase #3	$14.41	11.668%	$16.0914	$16.09	$16.10	$16.10
Purchase #4	$85.45	8.335%	$92.5723	$92.57	$92.55	$92.60
Purchase #5	$19.50	5.105%	$20.4955	$20.50	$20.50	$20.50
Purchase #6	$83.73	7.138%	$89.7066	$89.71	$89.70	$89.70
Purchase #7	$69.73	6.478%	$74.2471	$74.25	$74.25	$74.20
7 purchase totals =	$440.07		$480.1623	$480.17	$480.15	$480.10