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	$67.88	3.394%	$70.1838	$70.18	$70.20	$70.20
Purchase #2	$157.27	6.794%	$167.9549	$167.95	$167.95	$168.00
Purchase #3	$89.74	12.471%	$100.9315	$100.93	$100.95	$100.90
Purchase #4	$116.48	13.856%	$132.6195	$132.62	$132.60	$132.60
Purchase #5	$53.79	11.247%	$59.8398	$59.84	$59.85	$59.80
Purchase #6	$218.72	3.276%	$225.8853	$225.89	$225.90	$225.90
Purchase #7	$139.84	6.641%	$149.1268	$149.13	$149.15	$149.10
7 purchase totals =	$843.72		$906.5416	$906.54	$906.60	$906.50