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	$31.85	5.836%	$33.7088	$33.71	$33.70	$33.70
Purchase #2	$73.51	5.287%	$77.3965	$77.40	$77.40	$77.40
Purchase #3	$108.38	9.660%	$118.8495	$118.85	$118.85	$118.80
Purchase #4	$131.43	6.275%	$139.6772	$139.68	$139.70	$139.70
Purchase #5	$89.55	6.461%	$95.3358	$95.34	$95.35	$95.30
Purchase #6	$69.50	12.872%	$78.446	$78.45	$78.45	$78.40
Purchase #7	$82.97	5.166%	$87.2562	$87.26	$87.25	$87.30
7 purchase totals =	$587.19		$630.6700	$630.69	$630.70	$630.60