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	$172.40	11.776%	$192.7018	$192.70	$192.70	$192.70
Purchase #2	$172.52	4.287%	$179.9159	$179.92	$179.90	$179.90
Purchase #3	$241.78	12.821%	$272.7786	$272.78	$272.80	$272.80
Purchase #4	$127.96	6.373%	$136.1149	$136.11	$136.10	$136.10
Purchase #5	$10.48	12.404%	$11.7799	$11.78	$11.80	$11.80
Purchase #6	$70.88	10.303%	$78.1828	$78.18	$78.20	$78.20
Purchase #7	$53.61	6.589%	$57.1424	$57.14	$57.15	$57.10
7 purchase totals =	$849.63		$928.6163	$928.61	$928.65	$928.60