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	$40.77	4.803%	$42.7282	$42.73	$42.75	$42.70
Purchase #2	$134.77	5.754%	$142.5247	$142.52	$142.50	$142.50
Purchase #3	$84.54	3.536%	$87.5293	$87.53	$87.55	$87.50
Purchase #4	$250.42	3.610%	$259.4602	$259.46	$259.45	$259.50
Purchase #5	$116.82	12.336%	$131.2309	$131.23	$131.25	$131.20
Purchase #6	$156.75	11.759%	$175.1822	$175.18	$175.20	$175.20
Purchase #7	$52.76	6.590%	$56.2369	$56.24	$56.25	$56.20
7 purchase totals =	$836.83		$894.8924	$894.89	$894.95	$894.80