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	$104.39	6.807%	$111.4958	$111.50	$111.50	$111.50
Purchase #2	$62.56	10.355%	$69.0381	$69.04	$69.05	$69.00
Purchase #3	$111.91	5.637%	$118.2184	$118.22	$118.20	$118.20
Purchase #4	$85.48	7.339%	$91.7534	$91.75	$91.75	$91.80
Purchase #5	$234.80	13.147%	$265.6692	$265.67	$265.65	$265.70
Purchase #6	$162.45	3.344%	$167.8823	$167.88	$167.90	$167.90
Purchase #7	$123.85	3.608%	$128.3185	$128.32	$128.30	$128.30
7 purchase totals =	$885.44		$952.3757	$952.38	$952.35	$952.40