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	$250.74	9.368%	$274.2293	$274.23	$274.25	$274.20
Purchase #2	$144.75	9.482%	$158.4752	$158.48	$158.50	$158.50
Purchase #3	$101.28	11.344%	$112.7692	$112.77	$112.75	$112.80
Purchase #4	$99.80	5.531%	$105.3199	$105.32	$105.30	$105.30
Purchase #5	$227.70	7.628%	$245.069	$245.07	$245.05	$245.10
Purchase #6	$33.89	13.757%	$38.5522	$38.55	$38.55	$38.60
Purchase #7	$75.66	13.738%	$86.0542	$86.05	$86.05	$86.10
7 purchase totals =	$933.82		$1,020.4690	$1,020.47	$1,020.45	$1,020.60