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	$91.49	7.437%	$98.2941	$98.29	$98.30	$98.30
Purchase #2	$180.47	7.718%	$194.3987	$194.40	$194.40	$194.40
Purchase #3	$120.89	10.577%	$133.6765	$133.68	$133.70	$133.70
Purchase #4	$34.32	12.454%	$38.5942	$38.59	$38.60	$38.60
Purchase #5	$177.41	10.666%	$196.3326	$196.33	$196.35	$196.30
Purchase #6	$136.55	4.747%	$143.032	$143.03	$143.05	$143.00
Purchase #7	$163.65	6.219%	$173.8274	$173.83	$173.85	$173.80
7 purchase totals =	$904.78		$978.1555	$978.15	$978.25	$978.10