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	$42.51	13.276%	$48.1536	$48.15	$48.15	$48.20
Purchase #2	$49.64	9.386%	$54.2992	$54.30	$54.30	$54.30
Purchase #3	$130.54	11.379%	$145.3941	$145.39	$145.40	$145.40
Purchase #4	$165.57	11.351%	$184.3639	$184.36	$184.35	$184.40
Purchase #5	$48.31	11.202%	$53.7217	$53.72	$53.70	$53.70
Purchase #6	$37.76	4.423%	$39.4301	$39.43	$39.45	$39.40
Purchase #7	$188.98	13.825%	$215.1065	$215.11	$215.10	$215.10
7 purchase totals =	$663.31		$740.4691	$740.46	$740.45	$740.50