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	$102.46	8.787%	$111.4632	$111.46	$111.45	$111.50
Purchase #2	$76.72	12.464%	$86.2824	$86.28	$86.30	$86.30
Purchase #3	$61.62	4.731%	$64.5352	$64.54	$64.55	$64.50
Purchase #4	$208.31	9.862%	$228.8535	$228.85	$228.85	$228.90
Purchase #5	$16.99	9.108%	$18.5374	$18.54	$18.55	$18.50
Purchase #6	$246.32	4.589%	$257.6236	$257.62	$257.60	$257.60
Purchase #7	$54.76	12.575%	$61.6461	$61.65	$61.65	$61.60
7 purchase totals =	$767.18		$828.9414	$828.94	$828.95	$828.90