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	$199.99	7.508%	$215.0052	$215.01	$215.00	$215.00
Purchase #2	$172.70	13.720%	$196.3944	$196.39	$196.40	$196.40
Purchase #3	$37.77	8.167%	$40.8547	$40.85	$40.85	$40.90
Purchase #4	$144.52	10.619%	$159.8666	$159.87	$159.85	$159.90
Purchase #5	$148.94	9.262%	$162.7348	$162.73	$162.75	$162.70
Purchase #6	$212.54	12.227%	$238.5273	$238.53	$238.55	$238.50
Purchase #7	$8.53	12.133%	$9.5649	$9.56	$9.55	$9.60
7 purchase totals =	$924.99		$1,022.9479	$1,022.94	$1,022.95	$1,023.00