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	$89.51	11.201%	$99.536	$99.54	$99.55	$99.50
Purchase #2	$240.89	11.773%	$269.25	$269.25	$269.25	$269.30
Purchase #3	$93.28	3.806%	$96.8302	$96.83	$96.85	$96.80
Purchase #4	$47.53	6.182%	$50.4683	$50.47	$50.45	$50.50
Purchase #5	$8.39	6.184%	$8.9088	$8.91	$8.90	$8.90
Purchase #6	$14.90	12.463%	$16.757	$16.76	$16.75	$16.80
Purchase #7	$40.35	6.681%	$43.0458	$43.05	$43.05	$43.00
7 purchase totals =	$534.85		$584.7961	$584.81	$584.80	$584.80