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	$185.48	13.392%	$210.3195	$210.32	$210.30	$210.30
Purchase #2	$119.70	4.339%	$124.8938	$124.89	$124.90	$124.90
Purchase #3	$33.45	3.316%	$34.5592	$34.56	$34.55	$34.60
Purchase #4	$80.90	11.326%	$90.0627	$90.06	$90.05	$90.10
Purchase #5	$229.53	11.457%	$255.8273	$255.83	$255.85	$255.80
Purchase #6	$76.75	8.111%	$82.9752	$82.98	$83.00	$83.00
Purchase #7	$34.89	8.668%	$37.9143	$37.91	$37.90	$37.90
7 purchase totals =	$760.70		$836.5520	$836.55	$836.55	$836.60