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	$51.38	9.727%	$56.3777	$56.38	$56.40	$56.40
Purchase #2	$197.90	13.166%	$223.9555	$223.96	$223.95	$224.00
Purchase #3	$196.67	10.105%	$216.5435	$216.54	$216.55	$216.50
Purchase #4	$240.25	8.514%	$260.7049	$260.70	$260.70	$260.70
Purchase #5	$118.27	11.167%	$131.4772	$131.48	$131.50	$131.50
Purchase #6	$65.79	3.292%	$67.9558	$67.96	$67.95	$68.00
Purchase #7	$192.25	8.354%	$208.3106	$208.31	$208.30	$208.30
7 purchase totals =	$1,062.51		$1,165.3252	$1,165.33	$1,165.35	$1,165.40