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	$103.90	12.242%	$116.6194	$116.62	$116.60	$116.60
Purchase #2	$53.84	10.272%	$59.3704	$59.37	$59.35	$59.40
Purchase #3	$73.87	5.234%	$77.7364	$77.74	$77.75	$77.70
Purchase #4	$83.96	7.800%	$90.5089	$90.51	$90.50	$90.50
Purchase #5	$231.94	11.744%	$259.179	$259.18	$259.20	$259.20
Purchase #6	$43.50	5.669%	$45.966	$45.97	$45.95	$46.00
Purchase #7	$16.81	3.467%	$17.3928	$17.39	$17.40	$17.40
7 purchase totals =	$607.82		$666.7729	$666.78	$666.75	$666.80