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	$70.86	12.689%	$79.8514	$79.85	$79.85	$79.90
Purchase #2	$123.46	7.367%	$132.5553	$132.56	$132.55	$132.60
Purchase #3	$38.85	12.662%	$43.7692	$43.77	$43.75	$43.80
Purchase #4	$166.93	5.198%	$175.607	$175.61	$175.60	$175.60
Purchase #5	$104.84	11.175%	$116.5559	$116.56	$116.55	$116.60
Purchase #6	$202.63	9.256%	$221.3854	$221.39	$221.40	$221.40
Purchase #7	$51.78	4.589%	$54.1562	$54.16	$54.15	$54.20
7 purchase totals =	$759.35		$823.8804	$823.90	$823.85	$824.10