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	$241.71	13.213%	$273.6471	$273.65	$273.65	$273.60
Purchase #2	$159.39	5.686%	$168.4529	$168.45	$168.45	$168.50
Purchase #3	$236.55	11.535%	$263.836	$263.84	$263.85	$263.80
Purchase #4	$174.61	12.627%	$196.658	$196.66	$196.65	$196.70
Purchase #5	$118.76	8.190%	$128.4864	$128.49	$128.50	$128.50
Purchase #6	$103.52	5.203%	$108.9061	$108.91	$108.90	$108.90
Purchase #7	$192.82	5.493%	$203.4116	$203.41	$203.40	$203.40
7 purchase totals =	$1,227.36		$1,343.3981	$1,343.41	$1,343.40	$1,343.40