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	$89.33	11.819%	$99.8879	$99.89	$99.90	$99.90
Purchase #2	$32.53	10.466%	$35.9346	$35.93	$35.95	$35.90
Purchase #3	$53.25	6.289%	$56.5989	$56.60	$56.60	$56.60
Purchase #4	$182.99	7.527%	$196.7637	$196.76	$196.75	$196.80
Purchase #5	$187.51	3.313%	$193.7222	$193.72	$193.70	$193.70
Purchase #6	$7.89	5.352%	$8.3123	$8.31	$8.30	$8.30
Purchase #7	$38.97	7.726%	$41.9808	$41.98	$42.00	$42.00
7 purchase totals =	$592.47		$633.2004	$633.19	$633.20	$633.20