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	$108.93	9.628%	$119.4178	$119.42	$119.40	$119.40
Purchase #2	$110.92	6.223%	$117.8226	$117.82	$117.80	$117.80
Purchase #3	$125.93	12.139%	$141.2166	$141.22	$141.20	$141.20
Purchase #4	$185.89	5.495%	$196.1047	$196.10	$196.10	$196.10
Purchase #5	$66.52	8.475%	$72.1576	$72.16	$72.15	$72.20
Purchase #6	$248.68	3.625%	$257.6947	$257.69	$257.70	$257.70
Purchase #7	$219.62	12.659%	$247.4217	$247.42	$247.40	$247.40
7 purchase totals =	$1,066.49		$1,151.8357	$1,151.83	$1,151.75	$1,151.80