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	$96.54	3.525%	$99.943	$99.94	$99.95	$99.90
Purchase #2	$178.77	5.111%	$187.9069	$187.91	$187.90	$187.90
Purchase #3	$164.75	9.177%	$179.8691	$179.87	$179.85	$179.90
Purchase #4	$16.69	10.141%	$18.3825	$18.38	$18.40	$18.40
Purchase #5	$162.75	12.125%	$182.4834	$182.48	$182.50	$182.50
Purchase #6	$26.33	7.520%	$28.31	$28.31	$28.30	$28.30
Purchase #7	$175.95	5.248%	$185.1839	$185.18	$185.20	$185.20
7 purchase totals =	$821.78		$882.0788	$882.07	$882.10	$882.10