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	$10.84	9.525%	$11.8725	$11.87	$11.85	$11.90
Purchase #2	$36.81	8.850%	$40.0677	$40.07	$40.05	$40.10
Purchase #3	$166.97	7.733%	$179.8818	$179.88	$179.90	$179.90
Purchase #4	$18.54	4.296%	$19.3365	$19.34	$19.35	$19.30
Purchase #5	$68.73	4.626%	$71.9094	$71.91	$71.90	$71.90
Purchase #6	$64.61	11.748%	$72.2004	$72.20	$72.20	$72.20
Purchase #7	$202.71	4.767%	$212.3732	$212.37	$212.35	$212.40
7 purchase totals =	$569.21		$607.6415	$607.64	$607.60	$607.70