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	$219.91	13.648%	$249.9233	$249.92	$249.90	$249.90
Purchase #2	$214.74	11.109%	$238.5955	$238.60	$238.60	$238.60
Purchase #3	$82.29	8.178%	$89.0197	$89.02	$89.00	$89.00
Purchase #4	$182.89	3.528%	$189.3424	$189.34	$189.35	$189.30
Purchase #5	$234.54	6.180%	$249.0346	$249.03	$249.05	$249.00
Purchase #6	$46.40	3.151%	$47.8621	$47.86	$47.85	$47.90
Purchase #7	$247.46	4.223%	$257.9102	$257.91	$257.90	$257.90
7 purchase totals =	$1,228.23		$1,321.6878	$1,321.68	$1,321.65	$1,321.60