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	$29.53	12.717%	$33.2853	$33.29	$33.30	$33.30
Purchase #2	$27.95	5.688%	$29.5398	$29.54	$29.55	$29.50
Purchase #3	$37.61	7.422%	$40.4014	$40.40	$40.40	$40.40
Purchase #4	$112.68	4.625%	$117.8915	$117.89	$117.90	$117.90
Purchase #5	$145.96	5.402%	$153.8448	$153.84	$153.85	$153.80
Purchase #6	$79.46	7.527%	$85.441	$85.44	$85.45	$85.40
Purchase #7	$156.59	12.599%	$176.3188	$176.32	$176.30	$176.30
7 purchase totals =	$589.78		$636.7226	$636.72	$636.75	$636.60