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	$26.60	12.464%	$29.9154	$29.92	$29.90	$29.90
Purchase #2	$184.42	3.230%	$190.3768	$190.38	$190.40	$190.40
Purchase #3	$79.82	6.758%	$85.2142	$85.21	$85.20	$85.20
Purchase #4	$65.58	9.803%	$72.0088	$72.01	$72.00	$72.00
Purchase #5	$135.32	12.427%	$152.1362	$152.14	$152.15	$152.10
Purchase #6	$126.81	10.219%	$139.7687	$139.77	$139.75	$139.80
Purchase #7	$26.42	8.172%	$28.579	$28.58	$28.60	$28.60
7 purchase totals =	$644.97		$697.9991	$698.01	$698.00	$698.00