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	$24.29	4.201%	$25.3104	$25.31	$25.30	$25.30
Purchase #2	$24.90	8.581%	$27.0367	$27.04	$27.05	$27.00
Purchase #3	$85.59	8.452%	$92.8241	$92.82	$92.80	$92.80
Purchase #4	$54.34	13.767%	$61.821	$61.82	$61.80	$61.80
Purchase #5	$74.91	4.776%	$78.4877	$78.49	$78.50	$78.50
Purchase #6	$100.85	13.719%	$114.6856	$114.69	$114.70	$114.70
Purchase #7	$140.89	13.182%	$159.4621	$159.46	$159.45	$159.50
7 purchase totals =	$505.77		$559.6276	$559.63	$559.60	$559.60