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	$61.43	7.633%	$66.119	$66.12	$66.10	$66.10
Purchase #2	$179.50	10.526%	$198.3942	$198.39	$198.40	$198.40
Purchase #3	$6.84	13.690%	$7.7764	$7.78	$7.80	$7.80
Purchase #4	$27.76	12.189%	$31.1437	$31.14	$31.15	$31.10
Purchase #5	$19.84	7.713%	$21.3703	$21.37	$21.35	$21.40
Purchase #6	$94.51	5.373%	$99.588	$99.59	$99.60	$99.60
Purchase #7	$209.44	6.215%	$222.4567	$222.46	$222.45	$222.50
7 purchase totals =	$599.32		$646.8483	$646.85	$646.85	$646.90