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	$159.66	5.738%	$168.8213	$168.82	$168.80	$168.80
Purchase #2	$87.67	5.491%	$92.484	$92.48	$92.50	$92.50
Purchase #3	$134.36	10.872%	$148.9676	$148.97	$148.95	$149.00
Purchase #4	$189.86	3.267%	$196.0627	$196.06	$196.05	$196.10
Purchase #5	$96.62	7.456%	$103.824	$103.82	$103.80	$103.80
Purchase #6	$206.64	6.672%	$220.427	$220.43	$220.45	$220.40
Purchase #7	$190.83	10.174%	$210.245	$210.25	$210.25	$210.20
7 purchase totals =	$1,065.64		$1,140.8316	$1,140.83	$1,140.80	$1,140.80