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	$77.98	7.211%	$83.6031	$83.60	$83.60	$83.60
Purchase #2	$110.92	13.775%	$126.1992	$126.20	$126.20	$126.20
Purchase #3	$185.87	6.814%	$198.5352	$198.54	$198.55	$198.50
Purchase #4	$10.93	8.539%	$11.8633	$11.86	$11.85	$11.90
Purchase #5	$54.86	8.367%	$59.4501	$59.45	$59.45	$59.50
Purchase #6	$249.85	12.293%	$280.5641	$280.56	$280.55	$280.60
Purchase #7	$57.57	13.136%	$65.1324	$65.13	$65.15	$65.10
7 purchase totals =	$747.98		$825.3474	$825.34	$825.35	$825.40