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	$79.87	12.806%	$90.0982	$90.10	$90.10	$90.10
Purchase #2	$98.89	7.850%	$106.6529	$106.65	$106.65	$106.70
Purchase #3	$39.25	11.784%	$43.8752	$43.88	$43.90	$43.90
Purchase #4	$176.79	6.259%	$187.8553	$187.86	$187.85	$187.90
Purchase #5	$86.35	10.840%	$95.7103	$95.71	$95.70	$95.70
Purchase #6	$139.29	6.801%	$148.7631	$148.76	$148.75	$148.80
Purchase #7	$37.42	4.797%	$39.215	$39.22	$39.20	$39.20
7 purchase totals =	$657.86		$712.1700	$712.18	$712.15	$712.30