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	$137.40	3.217%	$141.8202	$141.82	$141.80	$141.80
Purchase #2	$105.62	6.518%	$112.5043	$112.50	$112.50	$112.50
Purchase #3	$77.84	9.408%	$85.1632	$85.16	$85.15	$85.20
Purchase #4	$170.36	5.414%	$179.5833	$179.58	$179.60	$179.60
Purchase #5	$244.98	12.417%	$275.3992	$275.40	$275.40	$275.40
Purchase #6	$119.26	6.382%	$126.8712	$126.87	$126.85	$126.90
Purchase #7	$159.87	10.225%	$176.2167	$176.22	$176.20	$176.20
7 purchase totals =	$1,015.33		$1,097.5581	$1,097.55	$1,097.50	$1,097.60