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	$249.65	11.644%	$278.7192	$278.72	$278.70	$278.70
Purchase #2	$83.33	3.196%	$85.9932	$85.99	$86.00	$86.00
Purchase #3	$192.61	10.739%	$213.2944	$213.29	$213.30	$213.30
Purchase #4	$219.52	3.562%	$227.3393	$227.34	$227.35	$227.30
Purchase #5	$114.42	11.772%	$127.8895	$127.89	$127.90	$127.90
Purchase #6	$88.94	12.570%	$100.1198	$100.12	$100.10	$100.10
Purchase #7	$231.99	6.775%	$247.7073	$247.71	$247.70	$247.70
7 purchase totals =	$1,180.46		$1,281.0627	$1,281.06	$1,281.05	$1,281.00