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	$74.71	9.774%	$82.0122	$82.01	$82.00	$82.00
Purchase #2	$131.61	11.238%	$146.4003	$146.40	$146.40	$146.40
Purchase #3	$112.30	5.764%	$118.773	$118.77	$118.75	$118.80
Purchase #4	$55.47	12.431%	$62.3655	$62.37	$62.35	$62.40
Purchase #5	$97.76	12.440%	$109.9213	$109.92	$109.90	$109.90
Purchase #6	$157.38	13.526%	$178.6672	$178.67	$178.65	$178.70
Purchase #7	$66.64	7.109%	$71.3774	$71.38	$71.40	$71.40
7 purchase totals =	$695.87		$769.5169	$769.52	$769.45	$769.60