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	$33.81	11.627%	$37.7411	$37.74	$37.75	$37.70
Purchase #2	$135.40	6.511%	$144.2159	$144.22	$144.20	$144.20
Purchase #3	$206.70	6.148%	$219.4079	$219.41	$219.40	$219.40
Purchase #4	$172.58	9.203%	$188.4625	$188.46	$188.45	$188.50
Purchase #5	$12.34	12.577%	$13.892	$13.89	$13.90	$13.90
Purchase #6	$136.93	10.730%	$151.6226	$151.62	$151.60	$151.60
Purchase #7	$204.85	9.151%	$223.5958	$223.60	$223.60	$223.60
7 purchase totals =	$902.61		$978.9378	$978.94	$978.90	$978.90