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	$150.50	6.830%	$160.7792	$160.78	$160.80	$160.80
Purchase #2	$54.26	11.859%	$60.6947	$60.69	$60.70	$60.70
Purchase #3	$139.54	9.272%	$152.4781	$152.48	$152.50	$152.50
Purchase #4	$155.46	13.662%	$176.6989	$176.70	$176.70	$176.70
Purchase #5	$115.87	6.563%	$123.4745	$123.47	$123.45	$123.50
Purchase #6	$239.48	6.734%	$255.6066	$255.61	$255.60	$255.60
Purchase #7	$18.92	11.605%	$21.1157	$21.12	$21.10	$21.10
7 purchase totals =	$874.03		$950.8477	$950.85	$950.85	$950.90