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	$84.69	7.158%	$90.7521	$90.75	$90.75	$90.80
Purchase #2	$157.42	7.203%	$168.759	$168.76	$168.75	$168.80
Purchase #3	$31.27	3.219%	$32.2766	$32.28	$32.30	$32.30
Purchase #4	$175.47	8.647%	$190.6429	$190.64	$190.65	$190.60
Purchase #5	$14.69	11.168%	$16.3306	$16.33	$16.35	$16.30
Purchase #6	$33.95	11.771%	$37.9463	$37.95	$37.95	$37.90
Purchase #7	$130.46	10.574%	$144.2548	$144.25	$144.25	$144.30
7 purchase totals =	$627.95		$680.9623	$680.96	$681.00	$681.00