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	$52.77	12.290%	$59.2554	$59.26	$59.25	$59.30
Purchase #2	$82.49	9.396%	$90.2408	$90.24	$90.25	$90.20
Purchase #3	$60.83	6.566%	$64.8241	$64.82	$64.80	$64.80
Purchase #4	$239.60	12.689%	$270.0028	$270.00	$270.00	$270.00
Purchase #5	$147.26	13.492%	$167.1283	$167.13	$167.15	$167.10
Purchase #6	$175.66	4.143%	$182.9376	$182.94	$182.95	$182.90
Purchase #7	$173.28	3.307%	$179.0104	$179.01	$179.00	$179.00
7 purchase totals =	$931.89		$1,013.3994	$1,013.40	$1,013.40	$1,013.30