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	$63.82	11.412%	$71.1031	$71.10	$71.10	$71.10
Purchase #2	$145.43	13.333%	$164.8202	$164.82	$164.80	$164.80
Purchase #3	$152.40	9.681%	$167.1538	$167.15	$167.15	$167.20
Purchase #4	$52.64	13.692%	$59.8475	$59.85	$59.85	$59.80
Purchase #5	$145.84	5.471%	$153.8189	$153.82	$153.80	$153.80
Purchase #6	$60.91	3.276%	$62.9054	$62.91	$62.90	$62.90
Purchase #7	$66.47	13.730%	$75.5963	$75.60	$75.60	$75.60
7 purchase totals =	$687.51		$755.2452	$755.25	$755.20	$755.20