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	$97.64	12.543%	$109.887	$109.89	$109.90	$109.90
Purchase #2	$152.67	3.446%	$157.931	$157.93	$157.95	$157.90
Purchase #3	$50.25	5.367%	$52.9469	$52.95	$52.95	$52.90
Purchase #4	$17.68	12.543%	$19.8976	$19.90	$19.90	$19.90
Purchase #5	$99.38	5.580%	$104.9254	$104.93	$104.95	$104.90
Purchase #6	$109.32	10.569%	$120.874	$120.87	$120.85	$120.90
Purchase #7	$84.48	13.456%	$95.8476	$95.85	$95.85	$95.80
7 purchase totals =	$611.42		$662.3095	$662.32	$662.35	$662.20