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	$226.88	12.189%	$254.5344	$254.53	$254.55	$254.50
Purchase #2	$209.48	11.544%	$233.6624	$233.66	$233.65	$233.70
Purchase #3	$166.90	3.146%	$172.1507	$172.15	$172.15	$172.20
Purchase #4	$33.45	13.826%	$38.0748	$38.07	$38.05	$38.10
Purchase #5	$43.59	7.571%	$46.8902	$46.89	$46.90	$46.90
Purchase #6	$125.72	3.833%	$130.5388	$130.54	$130.55	$130.50
Purchase #7	$42.55	3.541%	$44.0567	$44.06	$44.05	$44.10
7 purchase totals =	$848.57		$919.9080	$919.90	$919.90	$920.00