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	$52.47	8.468%	$56.9132	$56.91	$56.90	$56.90
Purchase #2	$30.72	10.548%	$33.9603	$33.96	$33.95	$34.00
Purchase #3	$187.40	4.401%	$195.6475	$195.65	$195.65	$195.60
Purchase #4	$65.33	8.802%	$71.0803	$71.08	$71.10	$71.10
Purchase #5	$127.85	11.735%	$142.8532	$142.85	$142.85	$142.90
Purchase #6	$137.72	4.164%	$143.4547	$143.45	$143.45	$143.50
Purchase #7	$39.88	5.211%	$41.9581	$41.96	$41.95	$42.00
7 purchase totals =	$641.37		$685.8673	$685.86	$685.85	$686.00