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	$96.60	3.617%	$100.094	$100.09	$100.10	$100.10
Purchase #2	$126.92	9.856%	$139.4292	$139.43	$139.45	$139.40
Purchase #3	$222.81	10.173%	$245.4765	$245.48	$245.50	$245.50
Purchase #4	$7.44	3.137%	$7.6734	$7.67	$7.65	$7.70
Purchase #5	$78.28	13.175%	$88.5934	$88.59	$88.60	$88.60
Purchase #6	$145.51	9.594%	$159.4702	$159.47	$159.45	$159.50
Purchase #7	$79.79	4.414%	$83.3119	$83.31	$83.30	$83.30
7 purchase totals =	$757.35		$824.0486	$824.04	$824.05	$824.10