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	$72.71	7.603%	$78.2381	$78.24	$78.25	$78.20
Purchase #2	$231.70	4.168%	$241.3573	$241.36	$241.35	$241.40
Purchase #3	$38.57	11.831%	$43.1332	$43.13	$43.15	$43.10
Purchase #4	$250.76	11.823%	$280.4074	$280.41	$280.40	$280.40
Purchase #5	$235.35	6.624%	$250.9396	$250.94	$250.95	$250.90
Purchase #6	$167.95	12.164%	$188.3794	$188.38	$188.40	$188.40
Purchase #7	$154.36	12.725%	$174.0023	$174.00	$174.00	$174.00
7 purchase totals =	$1,151.40		$1,256.4573	$1,256.46	$1,256.50	$1,256.40