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	$20.31	3.221%	$20.9642	$20.96	$20.95	$21.00
Purchase #2	$74.64	5.119%	$78.4608	$78.46	$78.45	$78.50
Purchase #3	$100.46	11.537%	$112.0501	$112.05	$112.05	$112.10
Purchase #4	$148.62	5.294%	$156.4879	$156.49	$156.50	$156.50
Purchase #5	$176.30	4.635%	$184.4715	$184.47	$184.45	$184.50
Purchase #6	$231.55	5.259%	$243.7272	$243.73	$243.75	$243.70
Purchase #7	$72.92	12.155%	$81.7834	$81.78	$81.80	$81.80
7 purchase totals =	$824.80		$877.9451	$877.94	$877.95	$878.10