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	$227.92	6.747%	$243.2978	$243.30	$243.30	$243.30
Purchase #2	$182.62	3.198%	$188.4602	$188.46	$188.45	$188.50
Purchase #3	$216.35	11.473%	$241.1718	$241.17	$241.15	$241.20
Purchase #4	$218.28	3.318%	$225.5225	$225.52	$225.50	$225.50
Purchase #5	$83.70	7.617%	$90.0754	$90.08	$90.10	$90.10
Purchase #6	$27.98	9.196%	$30.553	$30.55	$30.55	$30.60
Purchase #7	$40.72	12.462%	$45.7945	$45.79	$45.80	$45.80
7 purchase totals =	$997.57		$1,064.8752	$1,064.87	$1,064.85	$1,065.00