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	$117.66	11.553%	$131.2533	$131.25	$131.25	$131.30
Purchase #2	$103.74	7.607%	$111.6315	$111.63	$111.65	$111.60
Purchase #3	$89.55	10.291%	$98.7656	$98.77	$98.75	$98.80
Purchase #4	$187.85	4.167%	$195.6777	$195.68	$195.70	$195.70
Purchase #5	$160.25	12.364%	$180.0633	$180.06	$180.05	$180.10
Purchase #6	$84.33	6.178%	$89.5399	$89.54	$89.55	$89.50
Purchase #7	$245.68	12.716%	$276.9207	$276.92	$276.90	$276.90
7 purchase totals =	$989.06		$1,083.8520	$1,083.85	$1,083.85	$1,083.90