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	$35.47	10.122%	$39.0603	$39.06	$39.05	$39.10
Purchase #2	$63.39	13.807%	$72.1423	$72.14	$72.15	$72.10
Purchase #3	$142.55	5.163%	$149.9099	$149.91	$149.90	$149.90
Purchase #4	$243.55	11.590%	$271.7774	$271.78	$271.80	$271.80
Purchase #5	$78.92	8.205%	$85.3954	$85.40	$85.40	$85.40
Purchase #6	$51.70	3.585%	$53.5534	$53.55	$53.55	$53.60
Purchase #7	$113.89	11.745%	$127.2664	$127.27	$127.25	$127.30
7 purchase totals =	$729.47		$799.1051	$799.11	$799.10	$799.20