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	$88.34	12.480%	$99.3648	$99.36	$99.35	$99.40
Purchase #2	$30.45	9.451%	$33.3278	$33.33	$33.35	$33.30
Purchase #3	$210.79	3.384%	$217.9231	$217.92	$217.90	$217.90
Purchase #4	$164.89	10.233%	$181.7632	$181.76	$181.75	$181.80
Purchase #5	$63.95	4.335%	$66.7222	$66.72	$66.70	$66.70
Purchase #6	$5.60	12.654%	$6.3086	$6.31	$6.30	$6.30
Purchase #7	$37.76	6.108%	$40.0664	$40.07	$40.05	$40.10
7 purchase totals =	$601.78		$645.4761	$645.47	$645.40	$645.50