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	$45.70	6.752%	$48.7857	$48.79	$48.80	$48.80
Purchase #2	$77.88	13.310%	$88.2458	$88.25	$88.25	$88.20
Purchase #3	$6.82	6.384%	$7.2554	$7.26	$7.25	$7.30
Purchase #4	$92.66	12.487%	$104.2305	$104.23	$104.25	$104.20
Purchase #5	$10.53	13.267%	$11.927	$11.93	$11.95	$11.90
Purchase #6	$186.70	12.200%	$209.4774	$209.48	$209.50	$209.50
Purchase #7	$102.89	6.431%	$109.5069	$109.51	$109.50	$109.50
7 purchase totals =	$523.18		$579.4287	$579.45	$579.50	$579.40