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	$26.81	5.279%	$28.2253	$28.23	$28.25	$28.20
Purchase #2	$84.44	8.209%	$91.3717	$91.37	$91.35	$91.40
Purchase #3	$75.72	3.308%	$78.2248	$78.22	$78.20	$78.20
Purchase #4	$64.96	7.645%	$69.9262	$69.93	$69.95	$69.90
Purchase #5	$100.45	10.735%	$111.2333	$111.23	$111.25	$111.20
Purchase #6	$15.27	4.283%	$15.924	$15.92	$15.90	$15.90
Purchase #7	$140.99	8.439%	$152.8881	$152.89	$152.90	$152.90
7 purchase totals =	$508.64		$547.7934	$547.79	$547.80	$547.70