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	$111.31	6.546%	$118.5964	$118.60	$118.60	$118.60
Purchase #2	$143.28	12.233%	$160.8074	$160.81	$160.80	$160.80
Purchase #3	$52.72	8.782%	$57.3499	$57.35	$57.35	$57.30
Purchase #4	$61.55	7.722%	$66.3029	$66.30	$66.30	$66.30
Purchase #5	$35.48	10.464%	$39.1926	$39.19	$39.20	$39.20
Purchase #6	$208.33	11.165%	$231.59	$231.59	$231.60	$231.60
Purchase #7	$45.93	3.394%	$47.4889	$47.49	$47.50	$47.50
7 purchase totals =	$658.60		$721.3281	$721.33	$721.35	$721.30