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	$16.37	6.845%	$17.4905	$17.49	$17.50	$17.50
Purchase #2	$85.66	3.617%	$88.7583	$88.76	$88.75	$88.80
Purchase #3	$89.30	9.691%	$97.9541	$97.95	$97.95	$98.00
Purchase #4	$162.69	3.579%	$168.5127	$168.51	$168.50	$168.50
Purchase #5	$63.85	13.855%	$72.6964	$72.70	$72.70	$72.70
Purchase #6	$38.74	4.361%	$40.4295	$40.43	$40.45	$40.40
Purchase #7	$78.81	9.260%	$86.1078	$86.11	$86.10	$86.10
7 purchase totals =	$535.42		$571.9493	$571.95	$571.95	$572.00