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	$87.81	13.289%	$99.4791	$99.48	$99.50	$99.50
Purchase #2	$43.49	4.667%	$45.5197	$45.52	$45.50	$45.50
Purchase #3	$73.95	11.746%	$82.6362	$82.64	$82.65	$82.60
Purchase #4	$32.31	6.425%	$34.3859	$34.39	$34.40	$34.40
Purchase #5	$205.44	11.790%	$229.6614	$229.66	$229.65	$229.70
Purchase #6	$144.37	3.194%	$148.9812	$148.98	$149.00	$149.00
Purchase #7	$28.41	5.788%	$30.0544	$30.05	$30.05	$30.10
7 purchase totals =	$615.78		$670.7179	$670.72	$670.75	$670.80