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	$175.78	4.588%	$183.8448	$183.84	$183.85	$183.80
Purchase #2	$88.44	4.775%	$92.663	$92.66	$92.65	$92.70
Purchase #3	$11.95	5.455%	$12.6019	$12.60	$12.60	$12.60
Purchase #4	$231.29	12.309%	$259.7595	$259.76	$259.75	$259.80
Purchase #5	$87.51	13.475%	$99.302	$99.30	$99.30	$99.30
Purchase #6	$65.69	9.315%	$71.809	$71.81	$71.80	$71.80
Purchase #7	$76.57	6.384%	$81.4582	$81.46	$81.45	$81.50
7 purchase totals =	$737.23		$801.4384	$801.43	$801.40	$801.50