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	$239.86	3.751%	$248.8571	$248.86	$248.85	$248.90
Purchase #2	$135.89	4.380%	$141.842	$141.84	$141.85	$141.80
Purchase #3	$69.92	13.200%	$79.1494	$79.15	$79.15	$79.10
Purchase #4	$49.94	13.732%	$56.7978	$56.80	$56.80	$56.80
Purchase #5	$226.41	12.390%	$254.4622	$254.46	$254.45	$254.50
Purchase #6	$205.57	8.244%	$222.5172	$222.52	$222.50	$222.50
Purchase #7	$113.35	9.181%	$123.7567	$123.76	$123.75	$123.80
7 purchase totals =	$1,040.94		$1,127.3824	$1,127.39	$1,127.35	$1,127.40