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	$53.98	13.165%	$61.0865	$61.09	$61.10	$61.10
Purchase #2	$121.57	13.856%	$138.4147	$138.41	$138.40	$138.40
Purchase #3	$229.48	7.700%	$247.15	$247.15	$247.15	$247.20
Purchase #4	$37.38	5.429%	$39.4094	$39.41	$39.40	$39.40
Purchase #5	$80.27	12.574%	$90.3631	$90.36	$90.35	$90.40
Purchase #6	$190.98	13.234%	$216.2543	$216.25	$216.25	$216.30
Purchase #7	$176.87	7.688%	$190.4678	$190.47	$190.45	$190.50
7 purchase totals =	$890.53		$983.1458	$983.14	$983.10	$983.30