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	$130.52	5.528%	$137.7351	$137.74	$137.75	$137.70
Purchase #2	$28.70	4.263%	$29.9235	$29.92	$29.90	$29.90
Purchase #3	$106.45	6.137%	$112.9828	$112.98	$113.00	$113.00
Purchase #4	$26.59	5.195%	$27.9714	$27.97	$27.95	$28.00
Purchase #5	$229.92	8.239%	$248.8631	$248.86	$248.85	$248.90
Purchase #6	$181.48	8.137%	$196.247	$196.25	$196.25	$196.20
Purchase #7	$137.83	13.826%	$156.8864	$156.89	$156.90	$156.90
7 purchase totals =	$841.49		$910.6093	$910.61	$910.60	$910.60