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	$150.93	10.524%	$166.8139	$166.81	$166.80	$166.80
Purchase #2	$53.60	6.123%	$56.8819	$56.88	$56.90	$56.90
Purchase #3	$82.56	10.653%	$91.3551	$91.36	$91.35	$91.40
Purchase #4	$103.76	5.783%	$109.7604	$109.76	$109.75	$109.80
Purchase #5	$96.25	13.208%	$108.9627	$108.96	$108.95	$109.00
Purchase #6	$15.33	12.465%	$17.2409	$17.24	$17.25	$17.20
Purchase #7	$93.71	6.164%	$99.4863	$99.49	$99.50	$99.50
7 purchase totals =	$596.14		$650.5012	$650.50	$650.50	$650.60