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	$21.29	3.340%	$22.0011	$22.00	$22.00	$22.00
Purchase #2	$137.89	10.659%	$152.5877	$152.59	$152.60	$152.60
Purchase #3	$50.55	5.259%	$53.2084	$53.21	$53.20	$53.20
Purchase #4	$164.63	3.367%	$170.1731	$170.17	$170.15	$170.20
Purchase #5	$78.58	12.329%	$88.2681	$88.27	$88.25	$88.30
Purchase #6	$96.54	7.870%	$104.1377	$104.14	$104.15	$104.10
Purchase #7	$246.78	3.543%	$255.5234	$255.52	$255.50	$255.50
7 purchase totals =	$796.26		$845.8995	$845.90	$845.85	$845.90