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	$20.36	6.626%	$21.7091	$21.71	$21.70	$21.70
Purchase #2	$211.32	7.766%	$227.7311	$227.73	$227.75	$227.70
Purchase #3	$250.32	7.557%	$269.2367	$269.24	$269.25	$269.20
Purchase #4	$223.30	6.810%	$238.5067	$238.51	$238.50	$238.50
Purchase #5	$65.54	10.543%	$72.4499	$72.45	$72.45	$72.40
Purchase #6	$26.44	12.173%	$29.6585	$29.66	$29.65	$29.70
Purchase #7	$217.73	10.457%	$240.498	$240.50	$240.50	$240.50
7 purchase totals =	$1,015.01		$1,099.7900	$1,099.80	$1,099.80	$1,099.70