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	$71.50	11.730%	$79.887	$79.89	$79.90	$79.90
Purchase #2	$152.28	12.229%	$170.9023	$170.90	$170.90	$170.90
Purchase #3	$79.78	12.678%	$89.8945	$89.89	$89.90	$89.90
Purchase #4	$58.81	11.757%	$65.7243	$65.72	$65.70	$65.70
Purchase #5	$44.92	7.428%	$48.2567	$48.26	$48.25	$48.30
Purchase #6	$163.94	6.587%	$174.7387	$174.74	$174.75	$174.70
Purchase #7	$196.58	12.142%	$220.4487	$220.45	$220.45	$220.40
7 purchase totals =	$767.81		$849.8522	$849.85	$849.85	$849.80