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	$42.51	13.378%	$48.197	$48.20	$48.20	$48.20
Purchase #2	$165.43	10.549%	$182.8812	$182.88	$182.90	$182.90
Purchase #3	$56.72	13.811%	$64.5536	$64.55	$64.55	$64.60
Purchase #4	$41.28	11.200%	$45.9034	$45.90	$45.90	$45.90
Purchase #5	$19.43	10.240%	$21.4196	$21.42	$21.40	$21.40
Purchase #6	$108.45	13.750%	$123.3619	$123.36	$123.35	$123.40
Purchase #7	$155.88	5.671%	$164.72	$164.72	$164.70	$164.70
7 purchase totals =	$589.70		$651.0367	$651.03	$651.00	$651.10