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	$112.86	6.495%	$120.1903	$120.19	$120.20	$120.20
Purchase #2	$101.86	8.141%	$110.1524	$110.15	$110.15	$110.20
Purchase #3	$73.60	6.795%	$78.6011	$78.60	$78.60	$78.60
Purchase #4	$137.86	11.645%	$153.9138	$153.91	$153.90	$153.90
Purchase #5	$156.62	6.688%	$167.0947	$167.09	$167.10	$167.10
Purchase #6	$37.60	7.496%	$40.4185	$40.42	$40.40	$40.40
Purchase #7	$244.72	10.679%	$270.8536	$270.85	$270.85	$270.90
7 purchase totals =	$865.12		$941.2244	$941.21	$941.20	$941.30