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	$48.28	9.484%	$52.8589	$52.86	$52.85	$52.90
Purchase #2	$28.50	4.394%	$29.7523	$29.75	$29.75	$29.80
Purchase #3	$84.25	12.210%	$94.5369	$94.54	$94.55	$94.50
Purchase #4	$93.48	6.401%	$99.4637	$99.46	$99.45	$99.50
Purchase #5	$122.86	13.634%	$139.6107	$139.61	$139.60	$139.60
Purchase #6	$150.61	3.570%	$155.9868	$155.99	$156.00	$156.00
Purchase #7	$25.35	9.293%	$27.7058	$27.71	$27.70	$27.70
7 purchase totals =	$553.33		$599.9151	$599.92	$599.90	$600.00