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	$218.25	13.737%	$248.231	$248.23	$248.25	$248.20
Purchase #2	$83.54	7.631%	$89.9149	$89.91	$89.90	$89.90
Purchase #3	$232.68	4.388%	$242.89	$242.89	$242.90	$242.90
Purchase #4	$249.49	11.447%	$278.0491	$278.05	$278.05	$278.00
Purchase #5	$250.84	13.239%	$284.0487	$284.05	$284.05	$284.00
Purchase #6	$136.66	12.576%	$153.8464	$153.85	$153.85	$153.80
Purchase #7	$211.39	6.396%	$224.9105	$224.91	$224.90	$224.90
7 purchase totals =	$1,382.85		$1,521.8906	$1,521.89	$1,521.90	$1,521.70