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	$150.68	11.820%	$168.4904	$168.49	$168.50	$168.50
Purchase #2	$65.95	11.803%	$73.7341	$73.73	$73.75	$73.70
Purchase #3	$189.49	3.565%	$196.2453	$196.25	$196.25	$196.20
Purchase #4	$107.38	11.429%	$119.6525	$119.65	$119.65	$119.70
Purchase #5	$20.50	5.329%	$21.5924	$21.59	$21.60	$21.60
Purchase #6	$161.73	7.510%	$173.8759	$173.88	$173.90	$173.90
Purchase #7	$84.31	9.576%	$92.3835	$92.38	$92.40	$92.40
7 purchase totals =	$780.04		$845.9741	$845.97	$846.05	$846.00