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	$24.25	9.230%	$26.4883	$26.49	$26.50	$26.50
Purchase #2	$131.78	4.807%	$138.1147	$138.11	$138.10	$138.10
Purchase #3	$48.63	3.682%	$50.4206	$50.42	$50.40	$50.40
Purchase #4	$78.63	4.562%	$82.2171	$82.22	$82.20	$82.20
Purchase #5	$19.29	9.574%	$21.1368	$21.14	$21.15	$21.10
Purchase #6	$38.35	6.713%	$40.9244	$40.92	$40.90	$40.90
Purchase #7	$38.85	9.462%	$42.526	$42.53	$42.55	$42.50
7 purchase totals =	$379.78		$401.8279	$401.83	$401.80	$401.70