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	$244.33	4.576%	$255.5105	$255.51	$255.50	$255.50
Purchase #2	$15.84	8.629%	$17.2068	$17.21	$17.20	$17.20
Purchase #3	$221.85	10.534%	$245.2197	$245.22	$245.20	$245.20
Purchase #4	$200.92	7.404%	$215.7961	$215.80	$215.80	$215.80
Purchase #5	$118.85	9.741%	$130.4272	$130.43	$130.45	$130.40
Purchase #6	$87.64	12.288%	$98.4092	$98.41	$98.40	$98.40
Purchase #7	$111.27	11.339%	$123.8869	$123.89	$123.90	$123.90
7 purchase totals =	$1,000.70		$1,086.4564	$1,086.47	$1,086.45	$1,086.40