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	$55.58	6.580%	$59.2372	$59.24	$59.25	$59.20
Purchase #2	$136.59	6.321%	$145.2239	$145.22	$145.20	$145.20
Purchase #3	$221.46	3.714%	$229.685	$229.69	$229.70	$229.70
Purchase #4	$71.32	10.613%	$78.8892	$78.89	$78.90	$78.90
Purchase #5	$106.95	11.212%	$118.9412	$118.94	$118.95	$118.90
Purchase #6	$139.28	10.227%	$153.5242	$153.52	$153.50	$153.50
Purchase #7	$27.31	6.743%	$29.1515	$29.15	$29.15	$29.20
7 purchase totals =	$758.49		$814.6522	$814.65	$814.65	$814.60