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	$167.32	12.449%	$188.1497	$188.15	$188.15	$188.10
Purchase #2	$150.79	13.526%	$171.1859	$171.19	$171.20	$171.20
Purchase #3	$41.37	4.831%	$43.3686	$43.37	$43.35	$43.40
Purchase #4	$94.25	8.682%	$102.4328	$102.43	$102.45	$102.40
Purchase #5	$24.82	10.279%	$27.3712	$27.37	$27.35	$27.40
Purchase #6	$152.69	5.604%	$161.2467	$161.25	$161.25	$161.20
Purchase #7	$83.26	13.465%	$94.471	$94.47	$94.45	$94.50
7 purchase totals =	$714.50		$788.2259	$788.23	$788.20	$788.20