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	$245.83	8.650%	$267.0943	$267.09	$267.10	$267.10
Purchase #2	$138.34	10.514%	$152.8851	$152.89	$152.90	$152.90
Purchase #3	$96.88	9.171%	$105.7649	$105.76	$105.75	$105.80
Purchase #4	$78.43	6.450%	$83.4887	$83.49	$83.50	$83.50
Purchase #5	$175.78	8.473%	$190.6738	$190.67	$190.65	$190.70
Purchase #6	$55.33	7.429%	$59.4405	$59.44	$59.45	$59.40
Purchase #7	$79.52	10.436%	$87.8187	$87.82	$87.80	$87.80
7 purchase totals =	$870.11		$947.1660	$947.16	$947.15	$947.20