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	$9.77	9.338%	$10.6823	$10.68	$10.70	$10.70
Purchase #2	$120.46	6.183%	$127.908	$127.91	$127.90	$127.90
Purchase #3	$250.63	9.522%	$274.495	$274.50	$274.50	$274.50
Purchase #4	$209.39	10.741%	$231.8806	$231.88	$231.90	$231.90
Purchase #5	$85.95	5.607%	$90.7692	$90.77	$90.75	$90.80
Purchase #6	$192.87	11.608%	$215.2583	$215.26	$215.25	$215.30
Purchase #7	$201.77	7.313%	$216.5254	$216.53	$216.55	$216.50
7 purchase totals =	$1,070.84		$1,167.5188	$1,167.53	$1,167.55	$1,167.60