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	$105.54	10.682%	$116.8138	$116.81	$116.80	$116.80
Purchase #2	$163.59	8.118%	$176.8702	$176.87	$176.85	$176.90
Purchase #3	$160.60	7.328%	$172.3688	$172.37	$172.35	$172.40
Purchase #4	$123.64	10.415%	$136.5171	$136.52	$136.50	$136.50
Purchase #5	$16.82	9.345%	$18.3918	$18.39	$18.40	$18.40
Purchase #6	$67.85	13.603%	$77.0796	$77.08	$77.10	$77.10
Purchase #7	$67.51	8.339%	$73.1397	$73.14	$73.15	$73.10
7 purchase totals =	$705.55		$771.1810	$771.18	$771.15	$771.20