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	$109.91	8.130%	$118.8457	$118.85	$118.85	$118.80
Purchase #2	$225.54	12.384%	$253.4709	$253.47	$253.45	$253.50
Purchase #3	$35.30	7.256%	$37.8614	$37.86	$37.85	$37.90
Purchase #4	$132.72	3.385%	$137.2126	$137.21	$137.20	$137.20
Purchase #5	$201.72	6.633%	$215.1001	$215.10	$215.10	$215.10
Purchase #6	$132.79	3.289%	$137.1575	$137.16	$137.15	$137.20
Purchase #7	$189.92	5.407%	$200.189	$200.19	$200.20	$200.20
7 purchase totals =	$1,027.90		$1,099.8372	$1,099.84	$1,099.80	$1,099.90