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	$249.56	7.652%	$268.6563	$268.66	$268.65	$268.70
Purchase #2	$237.96	5.359%	$250.7123	$250.71	$250.70	$250.70
Purchase #3	$32.28	11.454%	$35.9774	$35.98	$36.00	$36.00
Purchase #4	$207.56	11.537%	$231.5062	$231.51	$231.50	$231.50
Purchase #5	$11.89	11.770%	$13.2895	$13.29	$13.30	$13.30
Purchase #6	$77.92	7.698%	$83.9183	$83.92	$83.90	$83.90
Purchase #7	$81.73	9.609%	$89.5834	$89.58	$89.60	$89.60
7 purchase totals =	$898.90		$973.6434	$973.65	$973.65	$973.70