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	$223.61	3.449%	$231.3223	$231.32	$231.30	$231.30
Purchase #2	$81.27	11.568%	$90.6713	$90.67	$90.65	$90.70
Purchase #3	$99.94	12.557%	$112.4895	$112.49	$112.50	$112.50
Purchase #4	$121.83	11.244%	$135.5286	$135.53	$135.55	$135.50
Purchase #5	$228.63	8.180%	$247.3319	$247.33	$247.35	$247.30
Purchase #6	$39.70	12.314%	$44.5887	$44.59	$44.60	$44.60
Purchase #7	$135.52	5.854%	$143.4533	$143.45	$143.45	$143.50
7 purchase totals =	$930.50		$1,005.3856	$1,005.38	$1,005.40	$1,005.40