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	$150.33	10.488%	$166.0966	$166.10	$166.10	$166.10
Purchase #2	$75.39	3.821%	$78.2707	$78.27	$78.25	$78.30
Purchase #3	$65.88	12.807%	$74.3173	$74.32	$74.30	$74.30
Purchase #4	$115.59	12.788%	$130.3716	$130.37	$130.35	$130.40
Purchase #5	$95.89	4.208%	$99.9251	$99.93	$99.95	$99.90
Purchase #6	$63.58	13.269%	$72.0164	$72.02	$72.00	$72.00
Purchase #7	$87.82	5.732%	$92.8538	$92.85	$92.85	$92.90
7 purchase totals =	$654.48		$713.8515	$713.86	$713.80	$713.90