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	$206.36	11.702%	$230.5082	$230.51	$230.50	$230.50
Purchase #2	$60.63	11.612%	$67.6704	$67.67	$67.65	$67.70
Purchase #3	$153.30	7.202%	$164.3407	$164.34	$164.35	$164.30
Purchase #4	$222.98	7.105%	$238.8227	$238.82	$238.80	$238.80
Purchase #5	$51.86	3.595%	$53.7244	$53.72	$53.70	$53.70
Purchase #6	$117.96	10.482%	$130.3246	$130.32	$130.30	$130.30
Purchase #7	$90.54	9.797%	$99.4102	$99.41	$99.40	$99.40
7 purchase totals =	$903.63		$984.8012	$984.79	$984.70	$984.70