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	$97.53	7.141%	$104.4946	$104.49	$104.50	$104.50
Purchase #2	$196.99	9.851%	$216.3955	$216.40	$216.40	$216.40
Purchase #3	$114.79	10.226%	$126.5284	$126.53	$126.55	$126.50
Purchase #4	$26.99	12.155%	$30.2706	$30.27	$30.25	$30.30
Purchase #5	$98.46	5.543%	$103.9176	$103.92	$103.90	$103.90
Purchase #6	$187.39	4.712%	$196.2198	$196.22	$196.20	$196.20
Purchase #7	$158.67	4.265%	$165.4373	$165.44	$165.45	$165.40
7 purchase totals =	$880.82		$943.2638	$943.27	$943.25	$943.20