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	$179.96	6.228%	$191.1679	$191.17	$191.15	$191.20
Purchase #2	$48.31	5.602%	$51.0163	$51.02	$51.00	$51.00
Purchase #3	$66.61	9.250%	$72.7714	$72.77	$72.75	$72.80
Purchase #4	$65.60	10.546%	$72.5182	$72.52	$72.50	$72.50
Purchase #5	$196.69	6.573%	$209.6184	$209.62	$209.60	$209.60
Purchase #6	$205.51	3.224%	$212.1356	$212.14	$212.15	$212.10
Purchase #7	$5.74	9.535%	$6.2873	$6.29	$6.30	$6.30
7 purchase totals =	$768.42		$815.5151	$815.53	$815.45	$815.50