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	$68.31	7.748%	$73.6027	$73.60	$73.60	$73.60
Purchase #2	$94.91	4.673%	$99.3451	$99.35	$99.35	$99.30
Purchase #3	$131.89	8.730%	$143.404	$143.40	$143.40	$143.40
Purchase #4	$89.27	13.517%	$101.3366	$101.34	$101.35	$101.30
Purchase #5	$46.37	4.570%	$48.4891	$48.49	$48.50	$48.50
Purchase #6	$87.70	10.742%	$97.1207	$97.12	$97.10	$97.10
Purchase #7	$97.45	9.122%	$106.3394	$106.34	$106.35	$106.30
7 purchase totals =	$615.90		$669.6376	$669.64	$669.65	$669.50