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	$66.61	6.679%	$71.0589	$71.06	$71.05	$71.10
Purchase #2	$113.73	4.582%	$118.9411	$118.94	$118.95	$118.90
Purchase #3	$146.72	13.145%	$166.0063	$166.01	$166.00	$166.00
Purchase #4	$22.67	9.851%	$24.9032	$24.90	$24.90	$24.90
Purchase #5	$47.65	9.414%	$52.1358	$52.14	$52.15	$52.10
Purchase #6	$11.46	13.572%	$13.0154	$13.02	$13.00	$13.00
Purchase #7	$53.51	13.778%	$60.8826	$60.88	$60.90	$60.90
7 purchase totals =	$462.35		$506.9433	$506.95	$506.95	$506.90