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	$87.54	13.597%	$99.4428	$99.44	$99.45	$99.40
Purchase #2	$138.36	7.607%	$148.885	$148.89	$148.90	$148.90
Purchase #3	$56.83	13.447%	$64.4719	$64.47	$64.45	$64.50
Purchase #4	$14.45	3.247%	$14.9192	$14.92	$14.90	$14.90
Purchase #5	$45.58	8.673%	$49.5332	$49.53	$49.55	$49.50
Purchase #6	$201.74	6.787%	$215.4321	$215.43	$215.45	$215.40
Purchase #7	$82.84	11.319%	$92.2167	$92.22	$92.20	$92.20
7 purchase totals =	$627.34		$684.9009	$684.90	$684.90	$684.80