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	$28.94	12.252%	$32.4857	$32.49	$32.50	$32.50
Purchase #2	$135.30	5.620%	$142.9039	$142.90	$142.90	$142.90
Purchase #3	$227.28	6.811%	$242.76	$242.76	$242.75	$242.80
Purchase #4	$162.92	10.679%	$180.3182	$180.32	$180.30	$180.30
Purchase #5	$132.38	5.662%	$139.8754	$139.88	$139.90	$139.90
Purchase #6	$54.32	8.331%	$58.8454	$58.85	$58.85	$58.80
Purchase #7	$90.41	12.741%	$101.9291	$101.93	$101.95	$101.90
7 purchase totals =	$831.55		$899.1177	$899.13	$899.15	$899.10