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	$33.68	11.384%	$37.5141	$37.51	$37.50	$37.50
Purchase #2	$172.73	7.420%	$185.5466	$185.55	$185.55	$185.50
Purchase #3	$232.44	10.115%	$255.9513	$255.95	$255.95	$256.00
Purchase #4	$209.25	11.144%	$232.5688	$232.57	$232.55	$232.60
Purchase #5	$100.95	11.134%	$112.1898	$112.19	$112.20	$112.20
Purchase #6	$170.27	10.253%	$187.7278	$187.73	$187.75	$187.70
Purchase #7	$165.25	13.195%	$187.0547	$187.05	$187.05	$187.10
7 purchase totals =	$1,084.57		$1,198.5531	$1,198.55	$1,198.55	$1,198.60