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	$73.83	12.269%	$82.8882	$82.89	$82.90	$82.90
Purchase #2	$50.76	4.152%	$52.8676	$52.87	$52.85	$52.90
Purchase #3	$129.87	10.617%	$143.6583	$143.66	$143.65	$143.70
Purchase #4	$6.81	3.618%	$7.0564	$7.06	$7.05	$7.10
Purchase #5	$194.88	4.356%	$203.369	$203.37	$203.35	$203.40
Purchase #6	$117.69	9.466%	$128.8305	$128.83	$128.85	$128.80
Purchase #7	$47.93	10.374%	$52.9023	$52.90	$52.90	$52.90
7 purchase totals =	$621.77		$671.5723	$671.58	$671.55	$671.70