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	$112.99	12.837%	$127.4945	$127.49	$127.50	$127.50
Purchase #2	$58.89	13.826%	$67.0321	$67.03	$67.05	$67.00
Purchase #3	$21.38	10.669%	$23.661	$23.66	$23.65	$23.70
Purchase #4	$82.39	7.489%	$88.5602	$88.56	$88.55	$88.60
Purchase #5	$237.72	7.863%	$256.4119	$256.41	$256.40	$256.40
Purchase #6	$47.81	7.326%	$51.3126	$51.31	$51.30	$51.30
Purchase #7	$213.36	8.584%	$231.6748	$231.67	$231.65	$231.70
7 purchase totals =	$774.54		$846.1471	$846.13	$846.10	$846.20