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	$66.51	10.378%	$73.4124	$73.41	$73.40	$73.40
Purchase #2	$38.34	6.501%	$40.8325	$40.83	$40.85	$40.80
Purchase #3	$17.87	9.401%	$19.55	$19.55	$19.55	$19.60
Purchase #4	$121.96	5.291%	$128.4129	$128.41	$128.40	$128.40
Purchase #5	$169.66	12.741%	$191.2764	$191.28	$191.30	$191.30
Purchase #6	$70.27	3.544%	$72.7604	$72.76	$72.75	$72.80
Purchase #7	$155.55	7.358%	$166.9954	$167.00	$167.00	$167.00
7 purchase totals =	$640.16		$693.2400	$693.24	$693.25	$693.30