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	$146.29	10.670%	$161.8991	$161.90	$161.90	$161.90
Purchase #2	$246.40	4.867%	$258.3923	$258.39	$258.40	$258.40
Purchase #3	$101.83	7.750%	$109.7218	$109.72	$109.70	$109.70
Purchase #4	$151.78	10.628%	$167.9112	$167.91	$167.90	$167.90
Purchase #5	$6.48	4.628%	$6.7799	$6.78	$6.80	$6.80
Purchase #6	$80.72	5.590%	$85.2322	$85.23	$85.25	$85.20
Purchase #7	$63.71	5.136%	$66.9821	$66.98	$67.00	$67.00
7 purchase totals =	$797.21		$856.9186	$856.91	$856.95	$856.90