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	$17.91	8.680%	$19.4646	$19.46	$19.45	$19.50
Purchase #2	$217.59	7.380%	$233.6481	$233.65	$233.65	$233.60
Purchase #3	$127.82	5.506%	$134.8578	$134.86	$134.85	$134.90
Purchase #4	$88.43	4.360%	$92.2855	$92.29	$92.30	$92.30
Purchase #5	$115.85	6.369%	$123.2285	$123.23	$123.25	$123.20
Purchase #6	$210.72	4.814%	$220.8641	$220.86	$220.85	$220.90
Purchase #7	$155.68	4.514%	$162.7074	$162.71	$162.70	$162.70
7 purchase totals =	$934.00		$987.0560	$987.06	$987.05	$987.10