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	$72.94	8.746%	$79.3193	$79.32	$79.30	$79.30
Purchase #2	$91.76	8.828%	$99.8606	$99.86	$99.85	$99.90
Purchase #3	$35.79	8.786%	$38.9345	$38.93	$38.95	$38.90
Purchase #4	$198.59	12.430%	$223.2747	$223.27	$223.25	$223.30
Purchase #5	$37.93	6.289%	$40.3154	$40.32	$40.30	$40.30
Purchase #6	$29.62	6.393%	$31.5136	$31.51	$31.50	$31.50
Purchase #7	$42.30	5.628%	$44.6806	$44.68	$44.70	$44.70
7 purchase totals =	$508.93		$557.8987	$557.89	$557.85	$557.90