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	$159.51	7.716%	$171.8178	$171.82	$171.80	$171.80
Purchase #2	$135.73	11.478%	$151.3091	$151.31	$151.30	$151.30
Purchase #3	$52.40	4.201%	$54.6013	$54.60	$54.60	$54.60
Purchase #4	$80.54	4.228%	$83.9452	$83.95	$83.95	$83.90
Purchase #5	$152.80	12.233%	$171.492	$171.49	$171.50	$171.50
Purchase #6	$55.95	11.663%	$62.4754	$62.48	$62.50	$62.50
Purchase #7	$74.95	5.106%	$78.7769	$78.78	$78.80	$78.80
7 purchase totals =	$711.88		$774.4177	$774.43	$774.45	$774.40