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	$66.28	6.230%	$70.4092	$70.41	$70.40	$70.40
Purchase #2	$116.90	12.126%	$131.0753	$131.08	$131.10	$131.10
Purchase #3	$86.46	3.575%	$89.5509	$89.55	$89.55	$89.60
Purchase #4	$97.28	6.498%	$103.6013	$103.60	$103.60	$103.60
Purchase #5	$119.66	11.454%	$133.3659	$133.37	$133.35	$133.40
Purchase #6	$58.42	3.365%	$60.3858	$60.39	$60.40	$60.40
Purchase #7	$18.72	3.728%	$19.4179	$19.42	$19.40	$19.40
7 purchase totals =	$563.72		$607.8063	$607.82	$607.80	$607.90