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	$35.35	8.137%	$38.2264	$38.23	$38.25	$38.20
Purchase #2	$105.29	7.611%	$113.3036	$113.30	$113.30	$113.30
Purchase #3	$217.76	7.803%	$234.7518	$234.75	$234.75	$234.80
Purchase #4	$70.55	11.219%	$78.465	$78.47	$78.45	$78.50
Purchase #5	$59.92	11.719%	$66.942	$66.94	$66.95	$66.90
Purchase #6	$35.55	5.861%	$37.6336	$37.63	$37.65	$37.60
Purchase #7	$244.28	9.665%	$267.8897	$267.89	$267.90	$267.90
7 purchase totals =	$768.70		$837.2121	$837.21	$837.25	$837.20