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	$166.80	12.866%	$188.2605	$188.26	$188.25	$188.30
Purchase #2	$80.36	6.618%	$85.6782	$85.68	$85.70	$85.70
Purchase #3	$77.45	5.373%	$81.6114	$81.61	$81.60	$81.60
Purchase #4	$149.71	5.216%	$157.5189	$157.52	$157.50	$157.50
Purchase #5	$238.68	6.614%	$254.4663	$254.47	$254.45	$254.50
Purchase #6	$66.56	7.857%	$71.7896	$71.79	$71.80	$71.80
Purchase #7	$213.75	4.566%	$223.5098	$223.51	$223.50	$223.50
7 purchase totals =	$993.31		$1,062.8347	$1,062.84	$1,062.80	$1,062.90