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	$239.85	12.612%	$270.0999	$270.10	$270.10	$270.10
Purchase #2	$123.94	6.519%	$132.0196	$132.02	$132.00	$132.00
Purchase #3	$245.33	6.344%	$260.8937	$260.89	$260.90	$260.90
Purchase #4	$128.92	12.156%	$144.5915	$144.59	$144.60	$144.60
Purchase #5	$100.93	8.358%	$109.3657	$109.37	$109.35	$109.40
Purchase #6	$175.92	5.559%	$185.6994	$185.70	$185.70	$185.70
Purchase #7	$75.69	8.657%	$82.2425	$82.24	$82.25	$82.20
7 purchase totals =	$1,090.58		$1,184.9123	$1,184.91	$1,184.90	$1,184.90