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	$53.79	10.538%	$59.4584	$59.46	$59.45	$59.50
Purchase #2	$14.33	7.603%	$15.4195	$15.42	$15.40	$15.40
Purchase #3	$246.44	8.576%	$267.5747	$267.57	$267.55	$267.60
Purchase #4	$198.27	12.285%	$222.6275	$222.63	$222.65	$222.60
Purchase #5	$19.93	4.329%	$20.7928	$20.79	$20.80	$20.80
Purchase #6	$143.54	5.714%	$151.7419	$151.74	$151.75	$151.70
Purchase #7	$46.88	11.650%	$52.3415	$52.34	$52.35	$52.30
7 purchase totals =	$723.18		$789.9563	$789.95	$789.95	$789.90