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	$50.38	6.839%	$53.8255	$53.83	$53.85	$53.80
Purchase #2	$22.62	10.557%	$25.008	$25.01	$25.00	$25.00
Purchase #3	$69.45	12.342%	$78.0215	$78.02	$78.00	$78.00
Purchase #4	$86.36	5.359%	$90.988	$90.99	$91.00	$91.00
Purchase #5	$87.47	4.128%	$91.0808	$91.08	$91.10	$91.10
Purchase #6	$18.62	9.609%	$20.4092	$20.41	$20.40	$20.40
Purchase #7	$121.65	10.603%	$134.5485	$134.55	$134.55	$134.50
7 purchase totals =	$456.55		$493.8815	$493.89	$493.90	$493.80