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	$122.43	6.809%	$130.7663	$130.77	$130.75	$130.80
Purchase #2	$129.68	10.517%	$143.3184	$143.32	$143.30	$143.30
Purchase #3	$184.38	6.761%	$196.8459	$196.85	$196.85	$196.80
Purchase #4	$60.48	3.287%	$62.468	$62.47	$62.45	$62.50
Purchase #5	$151.36	8.537%	$164.2816	$164.28	$164.30	$164.30
Purchase #6	$128.74	8.164%	$139.2503	$139.25	$139.25	$139.30
Purchase #7	$64.64	6.752%	$69.0045	$69.00	$69.00	$69.00
7 purchase totals =	$841.71		$905.9350	$905.94	$905.90	$906.00