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	$82.39	9.114%	$89.899	$89.90	$89.90	$89.90
Purchase #2	$206.65	4.741%	$216.4473	$216.45	$216.45	$216.40
Purchase #3	$60.69	7.391%	$65.1756	$65.18	$65.20	$65.20
Purchase #4	$174.84	11.294%	$194.5864	$194.59	$194.60	$194.60
Purchase #5	$90.29	5.147%	$94.9372	$94.94	$94.95	$94.90
Purchase #6	$22.68	9.610%	$24.8595	$24.86	$24.85	$24.90
Purchase #7	$44.28	6.751%	$47.2693	$47.27	$47.25	$47.30
7 purchase totals =	$681.82		$733.1743	$733.19	$733.20	$733.20