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	$10.39	13.352%	$11.7773	$11.78	$11.80	$11.80
Purchase #2	$95.28	8.226%	$103.1177	$103.12	$103.10	$103.10
Purchase #3	$192.93	3.199%	$199.1018	$199.10	$199.10	$199.10
Purchase #4	$229.33	5.119%	$241.0694	$241.07	$241.05	$241.10
Purchase #5	$91.67	8.769%	$99.7085	$99.71	$99.70	$99.70
Purchase #6	$221.25	5.361%	$233.1112	$233.11	$233.10	$233.10
Purchase #7	$238.83	6.496%	$254.3444	$254.34	$254.35	$254.30
7 purchase totals =	$1,079.68		$1,142.2303	$1,142.23	$1,142.20	$1,142.20