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	$189.33	4.360%	$197.5848	$197.58	$197.60	$197.60
Purchase #2	$77.73	9.649%	$85.2302	$85.23	$85.25	$85.20
Purchase #3	$164.54	13.694%	$187.0721	$187.07	$187.05	$187.10
Purchase #4	$85.99	10.629%	$95.1299	$95.13	$95.15	$95.10
Purchase #5	$18.32	9.237%	$20.0122	$20.01	$20.00	$20.00
Purchase #6	$194.46	11.711%	$217.2332	$217.23	$217.25	$217.20
Purchase #7	$100.48	10.477%	$111.0073	$111.01	$111.00	$111.00
7 purchase totals =	$830.85		$913.2697	$913.26	$913.30	$913.20