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	$51.63	8.547%	$56.0428	$56.04	$56.05	$56.00
Purchase #2	$200.43	7.721%	$215.9052	$215.91	$215.90	$215.90
Purchase #3	$199.80	4.690%	$209.1706	$209.17	$209.15	$209.20
Purchase #4	$25.94	7.554%	$27.8995	$27.90	$27.90	$27.90
Purchase #5	$46.30	11.425%	$51.5898	$51.59	$51.60	$51.60
Purchase #6	$58.71	10.602%	$64.9344	$64.93	$64.95	$64.90
Purchase #7	$86.82	4.751%	$90.9448	$90.94	$90.95	$90.90
7 purchase totals =	$669.63		$716.4871	$716.48	$716.50	$716.40