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	$12.40	11.163%	$13.7842	$13.78	$13.80	$13.80
Purchase #2	$174.27	9.748%	$191.2578	$191.26	$191.25	$191.30
Purchase #3	$77.27	8.599%	$83.9144	$83.91	$83.90	$83.90
Purchase #4	$131.82	10.588%	$145.7771	$145.78	$145.80	$145.80
Purchase #5	$202.86	7.357%	$217.7844	$217.78	$217.80	$217.80
Purchase #6	$83.43	7.580%	$89.754	$89.75	$89.75	$89.80
Purchase #7	$8.97	6.558%	$9.5583	$9.56	$9.55	$9.60
7 purchase totals =	$691.02		$751.8302	$751.82	$751.85	$752.00