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	$7.87	8.164%	$8.5125	$8.51	$8.50	$8.50
Purchase #2	$94.39	6.485%	$100.5112	$100.51	$100.50	$100.50
Purchase #3	$21.42	4.188%	$22.3171	$22.32	$22.30	$22.30
Purchase #4	$243.96	12.569%	$274.6233	$274.62	$274.60	$274.60
Purchase #5	$141.61	11.216%	$157.493	$157.49	$157.50	$157.50
Purchase #6	$35.28	13.657%	$40.0982	$40.10	$40.10	$40.10
Purchase #7	$60.96	5.639%	$64.3975	$64.40	$64.40	$64.40
7 purchase totals =	$605.49		$667.9528	$667.95	$667.90	$667.90