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	$81.36	12.548%	$91.5691	$91.57	$91.55	$91.60
Purchase #2	$50.36	11.524%	$56.1635	$56.16	$56.15	$56.20
Purchase #3	$11.90	13.743%	$13.5354	$13.54	$13.55	$13.50
Purchase #4	$130.90	6.799%	$139.7999	$139.80	$139.80	$139.80
Purchase #5	$166.43	11.353%	$185.3248	$185.32	$185.30	$185.30
Purchase #6	$234.89	10.211%	$258.8746	$258.87	$258.85	$258.90
Purchase #7	$110.39	7.594%	$118.773	$118.77	$118.75	$118.80
7 purchase totals =	$786.23		$864.0403	$864.03	$863.95	$864.10