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	$175.67	5.818%	$185.8905	$185.89	$185.90	$185.90
Purchase #2	$247.48	3.193%	$255.382	$255.38	$255.40	$255.40
Purchase #3	$22.25	3.140%	$22.9487	$22.95	$22.95	$22.90
Purchase #4	$127.39	11.323%	$141.8144	$141.81	$141.80	$141.80
Purchase #5	$155.87	4.246%	$162.4882	$162.49	$162.50	$162.50
Purchase #6	$94.76	10.651%	$104.8529	$104.85	$104.85	$104.90
Purchase #7	$36.37	3.174%	$37.5244	$37.52	$37.50	$37.50
7 purchase totals =	$859.79		$910.9011	$910.89	$910.90	$910.90