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	$29.82	8.748%	$32.4287	$32.43	$32.45	$32.40
Purchase #2	$170.63	5.272%	$179.6256	$179.63	$179.65	$179.60
Purchase #3	$216.54	8.476%	$234.8939	$234.89	$234.90	$234.90
Purchase #4	$158.33	13.380%	$179.5146	$179.51	$179.50	$179.50
Purchase #5	$24.52	6.514%	$26.1172	$26.12	$26.10	$26.10
Purchase #6	$33.41	12.395%	$37.5512	$37.55	$37.55	$37.60
Purchase #7	$180.76	10.831%	$200.3381	$200.34	$200.35	$200.30
7 purchase totals =	$814.01		$890.4693	$890.47	$890.50	$890.40