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	$235.88	6.759%	$251.8231	$251.82	$251.80	$251.80
Purchase #2	$182.83	4.815%	$191.6333	$191.63	$191.65	$191.60
Purchase #3	$130.32	8.369%	$141.2265	$141.23	$141.25	$141.20
Purchase #4	$244.42	4.336%	$255.0181	$255.02	$255.00	$255.00
Purchase #5	$142.75	11.787%	$159.5759	$159.58	$159.60	$159.60
Purchase #6	$111.81	10.227%	$123.2448	$123.24	$123.25	$123.20
Purchase #7	$148.96	11.662%	$166.3317	$166.33	$166.35	$166.30
7 purchase totals =	$1,196.97		$1,288.8534	$1,288.85	$1,288.90	$1,288.70