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	$217.56	4.754%	$227.9028	$227.90	$227.90	$227.90
Purchase #2	$124.43	5.833%	$131.688	$131.69	$131.70	$131.70
Purchase #3	$235.30	12.364%	$264.3925	$264.39	$264.40	$264.40
Purchase #4	$123.75	6.179%	$131.3965	$131.40	$131.40	$131.40
Purchase #5	$83.81	13.869%	$95.4336	$95.43	$95.45	$95.40
Purchase #6	$144.79	4.649%	$151.5213	$151.52	$151.50	$151.50
Purchase #7	$248.78	13.347%	$281.9847	$281.98	$282.00	$282.00
7 purchase totals =	$1,178.42		$1,284.3194	$1,284.31	$1,284.35	$1,284.30