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	$231.43	7.511%	$248.8127	$248.81	$248.80	$248.80
Purchase #2	$226.45	4.150%	$235.8477	$235.85	$235.85	$235.80
Purchase #3	$250.48	9.150%	$273.3989	$273.40	$273.40	$273.40
Purchase #4	$49.27	6.473%	$52.4592	$52.46	$52.45	$52.50
Purchase #5	$248.72	12.568%	$279.9791	$279.98	$280.00	$280.00
Purchase #6	$61.82	6.132%	$65.6108	$65.61	$65.60	$65.60
Purchase #7	$196.57	13.117%	$222.3541	$222.35	$222.35	$222.40
7 purchase totals =	$1,264.74		$1,378.4625	$1,378.46	$1,378.45	$1,378.50