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	$80.82	6.300%	$85.9117	$85.91	$85.90	$85.90
Purchase #2	$59.70	13.382%	$67.6891	$67.69	$67.70	$67.70
Purchase #3	$234.62	11.196%	$260.8881	$260.89	$260.90	$260.90
Purchase #4	$71.54	13.848%	$81.4469	$81.45	$81.45	$81.40
Purchase #5	$149.42	4.668%	$156.3949	$156.39	$156.40	$156.40
Purchase #6	$21.26	13.629%	$24.1575	$24.16	$24.15	$24.20
Purchase #7	$157.59	5.361%	$166.0384	$166.04	$166.05	$166.00
7 purchase totals =	$774.95		$842.5266	$842.53	$842.55	$842.50