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	$243.45	11.760%	$272.0797	$272.08	$272.10	$272.10
Purchase #2	$139.84	11.762%	$156.288	$156.29	$156.30	$156.30
Purchase #3	$150.68	3.279%	$155.6208	$155.62	$155.60	$155.60
Purchase #4	$192.49	13.752%	$218.9612	$218.96	$218.95	$219.00
Purchase #5	$75.51	3.832%	$78.4035	$78.40	$78.40	$78.40
Purchase #6	$34.76	13.137%	$39.3264	$39.33	$39.35	$39.30
Purchase #7	$137.28	5.738%	$145.1571	$145.16	$145.15	$145.20
7 purchase totals =	$974.01		$1,065.8367	$1,065.84	$1,065.85	$1,065.90