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	$78.65	4.626%	$82.2883	$82.29	$82.30	$82.30
Purchase #2	$82.27	10.396%	$90.8228	$90.82	$90.80	$90.80
Purchase #3	$128.63	11.380%	$143.2681	$143.27	$143.25	$143.30
Purchase #4	$153.77	7.421%	$165.1813	$165.18	$165.20	$165.20
Purchase #5	$124.75	5.759%	$131.9344	$131.93	$131.95	$131.90
Purchase #6	$154.69	5.181%	$162.7045	$162.70	$162.70	$162.70
Purchase #7	$122.33	5.607%	$129.189	$129.19	$129.20	$129.20
7 purchase totals =	$845.09		$905.3884	$905.38	$905.40	$905.40