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	$25.73	3.655%	$26.6704	$26.67	$26.65	$26.70
Purchase #2	$226.76	12.572%	$255.2683	$255.27	$255.25	$255.30
Purchase #3	$212.63	6.778%	$227.0421	$227.04	$227.05	$227.00
Purchase #4	$86.63	11.497%	$96.5899	$96.59	$96.60	$96.60
Purchase #5	$79.56	13.444%	$90.256	$90.26	$90.25	$90.30
Purchase #6	$119.39	11.500%	$133.1199	$133.12	$133.10	$133.10
Purchase #7	$141.52	5.726%	$149.6234	$149.62	$149.60	$149.60
7 purchase totals =	$892.22		$978.5700	$978.57	$978.50	$978.60