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	$24.50	11.483%	$27.3133	$27.31	$27.30	$27.30
Purchase #2	$155.92	11.695%	$174.1548	$174.15	$174.15	$174.20
Purchase #3	$104.35	9.524%	$114.2883	$114.29	$114.30	$114.30
Purchase #4	$134.48	13.393%	$152.4909	$152.49	$152.50	$152.50
Purchase #5	$50.70	8.314%	$54.9152	$54.92	$54.90	$54.90
Purchase #6	$63.55	3.712%	$65.909	$65.91	$65.90	$65.90
Purchase #7	$248.88	4.555%	$260.2165	$260.22	$260.20	$260.20
7 purchase totals =	$782.38		$849.2880	$849.29	$849.25	$849.30