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	$45.39	10.789%	$50.2871	$50.29	$50.30	$50.30
Purchase #2	$74.53	12.467%	$83.8217	$83.82	$83.80	$83.80
Purchase #3	$130.36	11.121%	$144.8573	$144.86	$144.85	$144.90
Purchase #4	$112.57	6.274%	$119.6326	$119.63	$119.65	$119.60
Purchase #5	$147.78	7.162%	$158.364	$158.36	$158.35	$158.40
Purchase #6	$28.25	11.850%	$31.5976	$31.60	$31.60	$31.60
Purchase #7	$189.58	5.179%	$199.3983	$199.40	$199.40	$199.40
7 purchase totals =	$728.46		$787.9586	$787.96	$787.95	$788.00