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	$97.73	10.809%	$108.2936	$108.29	$108.30	$108.30
Purchase #2	$164.53	7.123%	$176.2495	$176.25	$176.25	$176.20
Purchase #3	$132.67	13.241%	$150.2368	$150.24	$150.25	$150.20
Purchase #4	$145.62	11.469%	$162.3212	$162.32	$162.30	$162.30
Purchase #5	$165.81	3.343%	$171.353	$171.35	$171.35	$171.40
Purchase #6	$236.83	9.446%	$259.201	$259.20	$259.20	$259.20
Purchase #7	$189.71	3.796%	$196.9114	$196.91	$196.90	$196.90
7 purchase totals =	$1,132.90		$1,224.5665	$1,224.56	$1,224.55	$1,224.50