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	$89.63	12.268%	$100.6258	$100.63	$100.65	$100.60
Purchase #2	$58.88	4.639%	$61.6114	$61.61	$61.60	$61.60
Purchase #3	$31.88	11.355%	$35.5	$35.50	$35.50	$35.50
Purchase #4	$168.53	5.741%	$178.2053	$178.21	$178.20	$178.20
Purchase #5	$48.93	11.859%	$54.7326	$54.73	$54.75	$54.70
Purchase #6	$60.74	11.715%	$67.8557	$67.86	$67.85	$67.90
Purchase #7	$143.39	6.318%	$152.4494	$152.45	$152.45	$152.40
7 purchase totals =	$601.98		$650.9802	$650.99	$651.00	$650.90