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	$150.26	3.677%	$155.7851	$155.79	$155.80	$155.80
Purchase #2	$43.73	9.107%	$47.7125	$47.71	$47.70	$47.70
Purchase #3	$40.61	7.398%	$43.6143	$43.61	$43.60	$43.60
Purchase #4	$54.73	12.401%	$61.5171	$61.52	$61.50	$61.50
Purchase #5	$146.43	12.512%	$164.7513	$164.75	$164.75	$164.80
Purchase #6	$174.82	7.464%	$187.8686	$187.87	$187.85	$187.90
Purchase #7	$10.38	13.632%	$11.795	$11.80	$11.80	$11.80
7 purchase totals =	$620.96		$673.0439	$673.05	$673.00	$673.10