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	$79.99	13.639%	$90.8998	$90.90	$90.90	$90.90
Purchase #2	$158.62	8.291%	$171.7712	$171.77	$171.75	$171.80
Purchase #3	$204.28	13.665%	$232.1949	$232.19	$232.20	$232.20
Purchase #4	$71.78	9.758%	$78.7843	$78.78	$78.80	$78.80
Purchase #5	$45.69	8.343%	$49.5019	$49.50	$49.50	$49.50
Purchase #6	$29.50	11.159%	$32.7919	$32.79	$32.80	$32.80
Purchase #7	$79.57	4.807%	$83.3949	$83.39	$83.40	$83.40
7 purchase totals =	$669.43		$739.3389	$739.32	$739.35	$739.40