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	$52.54	6.264%	$55.8311	$55.83	$55.85	$55.80
Purchase #2	$231.90	13.375%	$262.9166	$262.92	$262.90	$262.90
Purchase #3	$33.65	10.401%	$37.1499	$37.15	$37.15	$37.10
Purchase #4	$182.71	11.326%	$203.4037	$203.40	$203.40	$203.40
Purchase #5	$72.47	7.694%	$78.0458	$78.05	$78.05	$78.00
Purchase #6	$52.74	4.870%	$55.3084	$55.31	$55.30	$55.30
Purchase #7	$153.83	6.806%	$164.2997	$164.30	$164.30	$164.30
7 purchase totals =	$779.84		$856.9552	$856.96	$856.95	$856.80