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	$10.91	11.752%	$12.1921	$12.19	$12.20	$12.20
Purchase #2	$188.53	4.362%	$196.7537	$196.75	$196.75	$196.80
Purchase #3	$40.71	7.828%	$43.8968	$43.90	$43.90	$43.90
Purchase #4	$38.79	11.490%	$43.247	$43.25	$43.25	$43.20
Purchase #5	$22.43	6.356%	$23.8557	$23.86	$23.85	$23.90
Purchase #6	$191.69	4.768%	$200.8298	$200.83	$200.85	$200.80
Purchase #7	$235.72	8.605%	$256.0037	$256.00	$256.00	$256.00
7 purchase totals =	$728.78		$776.7788	$776.78	$776.80	$776.80