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	$130.57	5.377%	$137.5907	$137.59	$137.60	$137.60
Purchase #2	$168.79	10.673%	$186.805	$186.81	$186.80	$186.80
Purchase #3	$201.35	10.436%	$222.3629	$222.36	$222.35	$222.40
Purchase #4	$30.61	12.380%	$34.3995	$34.40	$34.40	$34.40
Purchase #5	$176.96	11.285%	$196.9299	$196.93	$196.95	$196.90
Purchase #6	$230.78	4.285%	$240.6689	$240.67	$240.65	$240.70
Purchase #7	$240.81	5.593%	$254.2785	$254.28	$254.30	$254.30
7 purchase totals =	$1,179.87		$1,273.0354	$1,273.04	$1,273.05	$1,273.10