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	$54.79	6.439%	$58.3179	$58.32	$58.30	$58.30
Purchase #2	$48.75	4.541%	$50.9637	$50.96	$50.95	$51.00
Purchase #3	$168.32	7.265%	$180.5484	$180.55	$180.55	$180.50
Purchase #4	$228.66	7.793%	$246.4795	$246.48	$246.50	$246.50
Purchase #5	$38.99	10.108%	$42.9311	$42.93	$42.95	$42.90
Purchase #6	$204.83	4.548%	$214.1457	$214.15	$214.15	$214.10
Purchase #7	$88.59	11.800%	$99.0436	$99.04	$99.05	$99.00
7 purchase totals =	$832.93		$892.4299	$892.43	$892.45	$892.30