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	$89.45	7.584%	$96.2339	$96.23	$96.25	$96.20
Purchase #2	$213.43	5.626%	$225.4376	$225.44	$225.45	$225.40
Purchase #3	$103.85	5.461%	$109.5212	$109.52	$109.50	$109.50
Purchase #4	$83.68	12.737%	$94.3383	$94.34	$94.35	$94.30
Purchase #5	$183.62	12.590%	$206.7378	$206.74	$206.75	$206.70
Purchase #6	$113.62	11.850%	$127.084	$127.08	$127.10	$127.10
Purchase #7	$51.91	3.780%	$53.8722	$53.87	$53.85	$53.90
7 purchase totals =	$839.56		$913.2250	$913.22	$913.25	$913.10