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	$37.89	7.118%	$40.587	$40.59	$40.60	$40.60
Purchase #2	$41.48	9.169%	$45.2833	$45.28	$45.30	$45.30
Purchase #3	$240.57	11.240%	$267.6101	$267.61	$267.60	$267.60
Purchase #4	$60.82	4.579%	$63.6049	$63.60	$63.60	$63.60
Purchase #5	$72.44	12.158%	$81.2473	$81.25	$81.25	$81.20
Purchase #6	$69.92	6.168%	$74.2327	$74.23	$74.25	$74.20
Purchase #7	$220.38	3.465%	$228.0162	$228.02	$228.00	$228.00
7 purchase totals =	$743.50		$800.5815	$800.58	$800.60	$800.50