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	$217.59	10.747%	$240.9744	$240.97	$240.95	$241.00
Purchase #2	$22.61	6.461%	$24.0708	$24.07	$24.05	$24.10
Purchase #3	$197.42	9.276%	$215.7327	$215.73	$215.75	$215.70
Purchase #4	$114.45	12.681%	$128.9634	$128.96	$128.95	$129.00
Purchase #5	$75.85	3.640%	$78.6109	$78.61	$78.60	$78.60
Purchase #6	$85.38	6.461%	$90.8964	$90.90	$90.90	$90.90
Purchase #7	$57.44	9.471%	$62.8801	$62.88	$62.90	$62.90
7 purchase totals =	$770.74		$842.1287	$842.12	$842.10	$842.20