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	$79.33	13.599%	$90.1181	$90.12	$90.10	$90.10
Purchase #2	$146.55	3.322%	$151.4184	$151.42	$151.40	$151.40
Purchase #3	$19.76	5.683%	$20.883	$20.88	$20.90	$20.90
Purchase #4	$180.81	6.232%	$192.0781	$192.08	$192.10	$192.10
Purchase #5	$73.81	9.695%	$80.9659	$80.97	$80.95	$81.00
Purchase #6	$77.38	12.217%	$86.8335	$86.83	$86.85	$86.80
Purchase #7	$161.85	11.588%	$180.6052	$180.61	$180.60	$180.60
7 purchase totals =	$739.49		$802.9022	$802.91	$802.90	$802.90