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	$65.28	9.249%	$71.3177	$71.32	$71.30	$71.30
Purchase #2	$94.98	3.719%	$98.5123	$98.51	$98.50	$98.50
Purchase #3	$59.66	10.837%	$66.1254	$66.13	$66.15	$66.10
Purchase #4	$5.84	8.297%	$6.3245	$6.32	$6.30	$6.30
Purchase #5	$136.50	5.734%	$144.3269	$144.33	$144.35	$144.30
Purchase #6	$13.53	3.142%	$13.9551	$13.96	$13.95	$14.00
Purchase #7	$223.72	6.731%	$238.7786	$238.78	$238.80	$238.80
7 purchase totals =	$599.51		$639.3405	$639.35	$639.35	$639.30