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	$130.80	9.536%	$143.2731	$143.27	$143.25	$143.30
Purchase #2	$141.73	12.596%	$159.5823	$159.58	$159.60	$159.60
Purchase #3	$249.56	11.710%	$278.7835	$278.78	$278.80	$278.80
Purchase #4	$188.73	4.167%	$196.5944	$196.59	$196.60	$196.60
Purchase #5	$237.50	11.143%	$263.9646	$263.96	$263.95	$264.00
Purchase #6	$147.69	10.672%	$163.4515	$163.45	$163.45	$163.50
Purchase #7	$66.82	6.843%	$71.3925	$71.39	$71.40	$71.40
7 purchase totals =	$1,162.83		$1,277.0419	$1,277.02	$1,277.05	$1,277.20