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	$34.67	12.467%	$38.9923	$38.99	$39.00	$39.00
Purchase #2	$226.80	7.263%	$243.2725	$243.27	$243.25	$243.30
Purchase #3	$171.55	12.861%	$193.613	$193.61	$193.60	$193.60
Purchase #4	$7.60	11.237%	$8.454	$8.45	$8.45	$8.50
Purchase #5	$66.46	8.419%	$72.0553	$72.06	$72.05	$72.10
Purchase #6	$242.64	4.533%	$253.6389	$253.64	$253.65	$253.60
Purchase #7	$189.59	10.701%	$209.878	$209.88	$209.90	$209.90
7 purchase totals =	$939.31		$1,019.9040	$1,019.90	$1,019.90	$1,020.00