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	$221.95	8.356%	$240.4961	$240.50	$240.50	$240.50
Purchase #2	$136.90	5.306%	$144.1639	$144.16	$144.15	$144.20
Purchase #3	$104.83	3.592%	$108.5955	$108.60	$108.60	$108.60
Purchase #4	$229.36	6.201%	$243.5826	$243.58	$243.60	$243.60
Purchase #5	$167.61	9.677%	$183.8296	$183.83	$183.85	$183.80
Purchase #6	$221.77	10.870%	$245.8764	$245.88	$245.90	$245.90
Purchase #7	$127.35	5.288%	$134.0843	$134.08	$134.10	$134.10
7 purchase totals =	$1,209.77		$1,300.6284	$1,300.63	$1,300.70	$1,300.70