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	$98.88	3.500%	$102.3408	$102.34	$102.35	$102.30
Purchase #2	$223.67	7.306%	$240.0113	$240.01	$240.00	$240.00
Purchase #3	$146.66	12.455%	$164.9265	$164.93	$164.95	$164.90
Purchase #4	$25.56	13.438%	$28.9948	$28.99	$29.00	$29.00
Purchase #5	$157.52	8.756%	$171.3125	$171.31	$171.30	$171.30
Purchase #6	$73.60	9.221%	$80.3867	$80.39	$80.40	$80.40
Purchase #7	$100.51	10.557%	$111.1208	$111.12	$111.10	$111.10
7 purchase totals =	$826.40		$899.0934	$899.09	$899.10	$899.00