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	$210.35	6.260%	$223.5179	$223.52	$223.50	$223.50
Purchase #2	$91.45	4.803%	$95.8423	$95.84	$95.85	$95.80
Purchase #3	$140.27	8.705%	$152.4805	$152.48	$152.50	$152.50
Purchase #4	$128.65	13.605%	$146.1528	$146.15	$146.15	$146.20
Purchase #5	$31.72	12.348%	$35.6368	$35.64	$35.65	$35.60
Purchase #6	$72.91	3.271%	$75.2949	$75.29	$75.30	$75.30
Purchase #7	$146.91	8.559%	$159.484	$159.48	$159.50	$159.50
7 purchase totals =	$822.26		$888.4092	$888.40	$888.45	$888.40