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	$128.54	9.244%	$140.4222	$140.42	$140.40	$140.40
Purchase #2	$52.60	9.110%	$57.3919	$57.39	$57.40	$57.40
Purchase #3	$89.25	11.261%	$99.3004	$99.30	$99.30	$99.30
Purchase #4	$50.29	7.532%	$54.0778	$54.08	$54.10	$54.10
Purchase #5	$180.49	6.483%	$192.1912	$192.19	$192.20	$192.20
Purchase #6	$243.93	7.173%	$261.4271	$261.43	$261.45	$261.40
Purchase #7	$80.82	6.586%	$86.1428	$86.14	$86.15	$86.10
7 purchase totals =	$825.92		$890.9534	$890.95	$891.00	$890.90