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	$50.78	5.456%	$53.5506	$53.55	$53.55	$53.60
Purchase #2	$113.48	11.494%	$126.5234	$126.52	$126.50	$126.50
Purchase #3	$161.62	4.208%	$168.421	$168.42	$168.40	$168.40
Purchase #4	$250.41	13.237%	$283.5568	$283.56	$283.55	$283.60
Purchase #5	$57.75	12.856%	$65.1743	$65.17	$65.15	$65.20
Purchase #6	$82.45	7.809%	$88.8885	$88.89	$88.90	$88.90
Purchase #7	$89.59	11.454%	$99.8516	$99.85	$99.85	$99.90
7 purchase totals =	$806.08		$885.9662	$885.96	$885.90	$886.10