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	$30.39	10.198%	$33.4892	$33.49	$33.50	$33.50
Purchase #2	$203.45	4.477%	$212.5585	$212.56	$212.55	$212.60
Purchase #3	$144.90	12.192%	$162.5662	$162.57	$162.55	$162.60
Purchase #4	$91.78	9.343%	$100.355	$100.36	$100.35	$100.40
Purchase #5	$246.35	7.578%	$265.0184	$265.02	$265.00	$265.00
Purchase #6	$22.55	12.295%	$25.3225	$25.32	$25.30	$25.30
Purchase #7	$20.27	5.292%	$21.3427	$21.34	$21.35	$21.30
7 purchase totals =	$759.69		$820.6525	$820.66	$820.60	$820.70