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	$6.45	13.508%	$7.3213	$7.32	$7.30	$7.30
Purchase #2	$138.72	4.316%	$144.7072	$144.71	$144.70	$144.70
Purchase #3	$199.69	8.391%	$216.446	$216.45	$216.45	$216.40
Purchase #4	$95.45	3.439%	$98.7325	$98.73	$98.75	$98.70
Purchase #5	$83.90	7.470%	$90.1673	$90.17	$90.15	$90.20
Purchase #6	$43.95	10.850%	$48.7186	$48.72	$48.70	$48.70
Purchase #7	$172.73	6.791%	$184.4601	$184.46	$184.45	$184.50
7 purchase totals =	$740.89		$790.5530	$790.56	$790.50	$790.50