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	$191.80	8.691%	$208.4693	$208.47	$208.45	$208.50
Purchase #2	$53.81	10.349%	$59.3788	$59.38	$59.40	$59.40
Purchase #3	$179.32	7.669%	$193.0721	$193.07	$193.05	$193.10
Purchase #4	$149.51	12.641%	$168.4096	$168.41	$168.40	$168.40
Purchase #5	$159.26	8.799%	$173.2733	$173.27	$173.25	$173.30
Purchase #6	$174.57	3.417%	$180.5351	$180.54	$180.55	$180.50
Purchase #7	$230.25	3.443%	$238.1775	$238.18	$238.20	$238.20
7 purchase totals =	$1,138.52		$1,221.3157	$1,221.32	$1,221.30	$1,221.40