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	$82.64	8.268%	$89.4727	$89.47	$89.45	$89.50
Purchase #2	$234.32	9.304%	$256.1211	$256.12	$256.10	$256.10
Purchase #3	$150.31	10.769%	$166.4969	$166.50	$166.50	$166.50
Purchase #4	$103.45	13.727%	$117.6506	$117.65	$117.65	$117.70
Purchase #5	$169.38	8.348%	$183.5198	$183.52	$183.50	$183.50
Purchase #6	$48.44	7.199%	$51.9272	$51.93	$51.95	$51.90
Purchase #7	$218.56	12.266%	$245.3686	$245.37	$245.35	$245.40
7 purchase totals =	$1,007.10		$1,110.5569	$1,110.56	$1,110.50	$1,110.60