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	$9.45	7.278%	$10.1378	$10.14	$10.15	$10.10
Purchase #2	$77.52	12.592%	$87.2813	$87.28	$87.30	$87.30
Purchase #3	$73.57	11.347%	$81.918	$81.92	$81.90	$81.90
Purchase #4	$174.39	12.796%	$196.7049	$196.70	$196.70	$196.70
Purchase #5	$106.33	5.776%	$112.4716	$112.47	$112.45	$112.50
Purchase #6	$175.96	3.347%	$181.8494	$181.85	$181.85	$181.80
Purchase #7	$116.98	11.832%	$130.8211	$130.82	$130.80	$130.80
7 purchase totals =	$734.20		$801.1841	$801.18	$801.15	$801.10