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	$149.89	5.801%	$158.5851	$158.59	$158.60	$158.60
Purchase #2	$196.60	9.812%	$215.8904	$215.89	$215.90	$215.90
Purchase #3	$85.54	10.617%	$94.6218	$94.62	$94.60	$94.60
Purchase #4	$135.30	8.467%	$146.7559	$146.76	$146.75	$146.80
Purchase #5	$105.39	12.124%	$118.1675	$118.17	$118.15	$118.20
Purchase #6	$101.81	7.524%	$109.4702	$109.47	$109.45	$109.50
Purchase #7	$113.49	7.780%	$122.3195	$122.32	$122.30	$122.30
7 purchase totals =	$888.02		$965.8104	$965.82	$965.75	$965.90