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	$173.43	9.321%	$189.5954	$189.60	$189.60	$189.60
Purchase #2	$41.79	7.731%	$45.0208	$45.02	$45.00	$45.00
Purchase #3	$88.69	3.794%	$92.0549	$92.05	$92.05	$92.10
Purchase #4	$8.30	3.251%	$8.5698	$8.57	$8.55	$8.60
Purchase #5	$97.32	3.692%	$100.9131	$100.91	$100.90	$100.90
Purchase #6	$40.27	12.385%	$45.2574	$45.26	$45.25	$45.30
Purchase #7	$233.34	13.614%	$265.1069	$265.11	$265.10	$265.10
7 purchase totals =	$683.14		$746.5183	$746.52	$746.45	$746.60