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	$86.54	6.671%	$92.3131	$92.31	$92.30	$92.30
Purchase #2	$43.99	13.231%	$49.8103	$49.81	$49.80	$49.80
Purchase #3	$146.50	4.675%	$153.3489	$153.35	$153.35	$153.30
Purchase #4	$66.33	7.256%	$71.1429	$71.14	$71.15	$71.10
Purchase #5	$142.89	13.655%	$162.4016	$162.40	$162.40	$162.40
Purchase #6	$196.39	3.509%	$203.2813	$203.28	$203.30	$203.30
Purchase #7	$176.89	8.324%	$191.6143	$191.61	$191.60	$191.60
7 purchase totals =	$859.53		$923.9124	$923.90	$923.90	$923.80