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	$132.84	4.294%	$138.5441	$138.54	$138.55	$138.50
Purchase #2	$80.43	10.650%	$88.9958	$89.00	$89.00	$89.00
Purchase #3	$216.76	3.211%	$223.7202	$223.72	$223.70	$223.70
Purchase #4	$236.85	12.178%	$265.6936	$265.69	$265.70	$265.70
Purchase #5	$149.48	12.707%	$168.4744	$168.47	$168.45	$168.50
Purchase #6	$168.60	11.668%	$188.2722	$188.27	$188.25	$188.30
Purchase #7	$176.60	11.259%	$196.4834	$196.48	$196.50	$196.50
7 purchase totals =	$1,161.56		$1,270.1837	$1,270.17	$1,270.15	$1,270.20