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	$36.68	9.812%	$40.279	$40.28	$40.30	$40.30
Purchase #2	$64.26	4.813%	$67.3528	$67.35	$67.35	$67.40
Purchase #3	$185.44	5.761%	$196.1232	$196.12	$196.10	$196.10
Purchase #4	$147.75	7.252%	$158.4648	$158.46	$158.45	$158.50
Purchase #5	$131.36	11.818%	$146.8841	$146.88	$146.90	$146.90
Purchase #6	$213.78	4.765%	$223.9666	$223.97	$223.95	$224.00
Purchase #7	$131.69	11.221%	$146.4669	$146.47	$146.45	$146.50
7 purchase totals =	$910.96		$979.5374	$979.53	$979.50	$979.70