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	$137.55	13.279%	$155.8153	$155.82	$155.80	$155.80
Purchase #2	$239.63	6.812%	$255.9536	$255.95	$255.95	$256.00
Purchase #3	$154.60	9.333%	$169.0288	$169.03	$169.05	$169.00
Purchase #4	$108.74	11.653%	$121.4115	$121.41	$121.40	$121.40
Purchase #5	$195.60	10.870%	$216.8617	$216.86	$216.85	$216.90
Purchase #6	$70.66	10.510%	$78.0864	$78.09	$78.10	$78.10
Purchase #7	$92.52	11.187%	$102.8702	$102.87	$102.85	$102.90
7 purchase totals =	$999.30		$1,100.0275	$1,100.03	$1,100.00	$1,100.10