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	$62.32	13.723%	$70.8722	$70.87	$70.85	$70.90
Purchase #2	$95.69	10.514%	$105.7508	$105.75	$105.75	$105.80
Purchase #3	$56.25	5.529%	$59.3601	$59.36	$59.35	$59.40
Purchase #4	$126.39	6.803%	$134.9883	$134.99	$135.00	$135.00
Purchase #5	$39.63	6.587%	$42.2404	$42.24	$42.25	$42.20
Purchase #6	$200.39	12.572%	$225.583	$225.58	$225.60	$225.60
Purchase #7	$147.89	4.823%	$155.0227	$155.02	$155.00	$155.00
7 purchase totals =	$728.56		$793.8175	$793.81	$793.80	$793.90