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	$98.88	8.322%	$107.1088	$107.11	$107.10	$107.10
Purchase #2	$217.42	12.451%	$244.491	$244.49	$244.50	$244.50
Purchase #3	$73.56	7.110%	$78.7901	$78.79	$78.80	$78.80
Purchase #4	$133.45	13.326%	$151.2335	$151.23	$151.25	$151.20
Purchase #5	$175.78	6.287%	$186.8313	$186.83	$186.85	$186.80
Purchase #6	$86.77	5.869%	$91.8625	$91.86	$91.85	$91.90
Purchase #7	$94.92	7.305%	$101.8539	$101.85	$101.85	$101.90
7 purchase totals =	$880.78		$962.1711	$962.16	$962.20	$962.20