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	$148.92	8.837%	$162.0801	$162.08	$162.10	$162.10
Purchase #2	$114.73	4.488%	$119.8791	$119.88	$119.90	$119.90
Purchase #3	$61.86	11.704%	$69.1001	$69.10	$69.10	$69.10
Purchase #4	$46.80	12.273%	$52.5438	$52.54	$52.55	$52.50
Purchase #5	$143.45	11.115%	$159.3945	$159.39	$159.40	$159.40
Purchase #6	$50.77	7.550%	$54.6031	$54.60	$54.60	$54.60
Purchase #7	$41.48	4.149%	$43.201	$43.20	$43.20	$43.20
7 purchase totals =	$608.01		$660.8017	$660.79	$660.85	$660.80