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	$72.79	6.493%	$77.5163	$77.52	$77.50	$77.50
Purchase #2	$47.44	11.448%	$52.8709	$52.87	$52.85	$52.90
Purchase #3	$213.33	6.604%	$227.4183	$227.42	$227.40	$227.40
Purchase #4	$234.59	9.619%	$257.1552	$257.16	$257.15	$257.20
Purchase #5	$86.60	7.706%	$93.2734	$93.27	$93.25	$93.30
Purchase #6	$171.32	8.397%	$185.7057	$185.71	$185.70	$185.70
Purchase #7	$95.72	13.158%	$108.3148	$108.31	$108.30	$108.30
7 purchase totals =	$921.79		$1,002.2546	$1,002.26	$1,002.15	$1,002.30