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	$50.89	13.771%	$57.8981	$57.90	$57.90	$57.90
Purchase #2	$139.27	7.805%	$150.14	$150.14	$150.15	$150.10
Purchase #3	$73.45	11.229%	$81.6977	$81.70	$81.70	$81.70
Purchase #4	$68.93	10.336%	$76.0546	$76.05	$76.05	$76.10
Purchase #5	$76.48	5.769%	$80.8921	$80.89	$80.90	$80.90
Purchase #6	$150.50	12.156%	$168.7948	$168.79	$168.80	$168.80
Purchase #7	$107.70	3.196%	$111.1421	$111.14	$111.15	$111.10
7 purchase totals =	$667.22		$726.6194	$726.61	$726.65	$726.60