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	$56.84	12.356%	$63.8632	$63.86	$63.85	$63.90
Purchase #2	$148.34	13.363%	$168.1627	$168.16	$168.15	$168.20
Purchase #3	$132.94	13.565%	$150.9733	$150.97	$150.95	$151.00
Purchase #4	$63.46	6.521%	$67.5982	$67.60	$67.60	$67.60
Purchase #5	$38.61	9.737%	$42.3695	$42.37	$42.35	$42.40
Purchase #6	$180.74	8.601%	$196.2854	$196.29	$196.30	$196.30
Purchase #7	$230.80	3.272%	$238.3518	$238.35	$238.35	$238.40
7 purchase totals =	$851.73		$927.6041	$927.60	$927.55	$927.80