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	$63.38	3.658%	$65.6984	$65.70	$65.70	$65.70
Purchase #2	$155.56	11.607%	$173.6158	$173.62	$173.60	$173.60
Purchase #3	$112.91	6.783%	$120.5687	$120.57	$120.55	$120.60
Purchase #4	$121.61	4.756%	$127.3938	$127.39	$127.40	$127.40
Purchase #5	$238.47	12.290%	$267.778	$267.78	$267.80	$267.80
Purchase #6	$64.77	4.317%	$67.5661	$67.57	$67.55	$67.60
Purchase #7	$91.46	13.213%	$103.5446	$103.54	$103.55	$103.50
7 purchase totals =	$848.16		$926.1654	$926.17	$926.15	$926.20