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	$42.56	3.172%	$43.91	$43.91	$43.90	$43.90
Purchase #2	$71.57	8.375%	$77.564	$77.56	$77.55	$77.60
Purchase #3	$102.87	5.824%	$108.8611	$108.86	$108.85	$108.90
Purchase #4	$133.81	4.553%	$139.9024	$139.90	$139.90	$139.90
Purchase #5	$121.27	3.411%	$125.4065	$125.41	$125.40	$125.40
Purchase #6	$42.51	5.587%	$44.885	$44.89	$44.90	$44.90
Purchase #7	$78.26	8.644%	$85.0248	$85.02	$85.00	$85.00
7 purchase totals =	$592.85		$625.5538	$625.55	$625.50	$625.60