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	$17.70	13.870%	$20.155	$20.16	$20.15	$20.20
Purchase #2	$155.96	6.637%	$166.3111	$166.31	$166.30	$166.30
Purchase #3	$176.63	3.533%	$182.8703	$182.87	$182.85	$182.90
Purchase #4	$157.74	10.823%	$174.8122	$174.81	$174.80	$174.80
Purchase #5	$113.62	11.757%	$126.9783	$126.98	$127.00	$127.00
Purchase #6	$65.95	10.569%	$72.9203	$72.92	$72.90	$72.90
Purchase #7	$10.30	10.400%	$11.3712	$11.37	$11.35	$11.40
7 purchase totals =	$697.90		$755.4184	$755.42	$755.35	$755.50