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	$132.60	5.467%	$139.8492	$139.85	$139.85	$139.80
Purchase #2	$75.54	3.462%	$78.1552	$78.16	$78.15	$78.20
Purchase #3	$42.41	10.693%	$46.9449	$46.94	$46.95	$46.90
Purchase #4	$103.78	9.186%	$113.3132	$113.31	$113.30	$113.30
Purchase #5	$204.63	3.732%	$212.2668	$212.27	$212.25	$212.30
Purchase #6	$6.68	6.826%	$7.136	$7.14	$7.15	$7.10
Purchase #7	$40.57	8.173%	$43.8858	$43.89	$43.90	$43.90
7 purchase totals =	$606.21		$641.5511	$641.56	$641.55	$641.50