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	$34.98	7.499%	$37.6032	$37.60	$37.60	$37.60
Purchase #2	$41.72	13.140%	$47.202	$47.20	$47.20	$47.20
Purchase #3	$136.59	4.555%	$142.8117	$142.81	$142.80	$142.80
Purchase #4	$15.94	10.113%	$17.552	$17.55	$17.55	$17.60
Purchase #5	$105.26	4.354%	$109.843	$109.84	$109.85	$109.80
Purchase #6	$126.72	9.704%	$139.0169	$139.02	$139.00	$139.00
Purchase #7	$26.91	3.606%	$27.8804	$27.88	$27.90	$27.90
7 purchase totals =	$488.12		$521.9092	$521.90	$521.90	$521.90