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	$144.69	13.830%	$164.7006	$164.70	$164.70	$164.70
Purchase #2	$35.77	12.134%	$40.1103	$40.11	$40.10	$40.10
Purchase #3	$108.69	5.500%	$114.668	$114.67	$114.65	$114.70
Purchase #4	$155.47	7.801%	$167.5982	$167.60	$167.60	$167.60
Purchase #5	$81.59	7.719%	$87.8879	$87.89	$87.90	$87.90
Purchase #6	$83.46	7.699%	$89.8856	$89.89	$89.90	$89.90
Purchase #7	$56.34	3.232%	$58.1609	$58.16	$58.15	$58.20
7 purchase totals =	$666.01		$723.0115	$723.02	$723.00	$723.10