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	$181.74	9.609%	$199.2034	$199.20	$199.20	$199.20
Purchase #2	$165.30	11.786%	$184.7823	$184.78	$184.80	$184.80
Purchase #3	$250.74	6.320%	$266.5868	$266.59	$266.60	$266.60
Purchase #4	$41.37	3.775%	$42.9317	$42.93	$42.95	$42.90
Purchase #5	$38.70	8.515%	$41.9953	$42.00	$42.00	$42.00
Purchase #6	$101.98	9.251%	$111.4142	$111.41	$111.40	$111.40
Purchase #7	$133.53	6.261%	$141.8903	$141.89	$141.90	$141.90
7 purchase totals =	$913.36		$988.8040	$988.80	$988.85	$988.80