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	$105.92	13.690%	$120.4204	$120.42	$120.40	$120.40
Purchase #2	$40.67	4.373%	$42.4485	$42.45	$42.45	$42.40
Purchase #3	$52.35	4.470%	$54.69	$54.69	$54.70	$54.70
Purchase #4	$123.83	6.504%	$131.8839	$131.88	$131.90	$131.90
Purchase #5	$210.30	7.326%	$225.7066	$225.71	$225.70	$225.70
Purchase #6	$12.57	3.562%	$13.0177	$13.02	$13.00	$13.00
Purchase #7	$88.91	10.565%	$98.3033	$98.30	$98.30	$98.30
7 purchase totals =	$634.55		$686.4704	$686.47	$686.45	$686.40