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	$198.73	12.681%	$223.931	$223.93	$223.95	$223.90
Purchase #2	$191.56	10.398%	$211.4784	$211.48	$211.50	$211.50
Purchase #3	$130.53	5.570%	$137.8005	$137.80	$137.80	$137.80
Purchase #4	$38.32	5.602%	$40.4667	$40.47	$40.45	$40.50
Purchase #5	$72.35	3.442%	$74.8403	$74.84	$74.85	$74.80
Purchase #6	$250.92	11.453%	$279.6579	$279.66	$279.65	$279.70
Purchase #7	$30.98	8.448%	$33.5972	$33.60	$33.60	$33.60
7 purchase totals =	$913.39		$1,001.7720	$1,001.78	$1,001.80	$1,001.80