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	$127.73	12.601%	$143.8253	$143.83	$143.85	$143.80
Purchase #2	$120.98	7.744%	$130.3487	$130.35	$130.35	$130.30
Purchase #3	$196.70	4.687%	$205.9193	$205.92	$205.90	$205.90
Purchase #4	$135.45	7.261%	$145.285	$145.29	$145.30	$145.30
Purchase #5	$101.55	6.340%	$107.9883	$107.99	$108.00	$108.00
Purchase #6	$33.75	10.566%	$37.316	$37.32	$37.30	$37.30
Purchase #7	$101.85	7.455%	$109.4429	$109.44	$109.45	$109.40
7 purchase totals =	$818.01		$880.1255	$880.14	$880.15	$880.00