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	$127.34	7.155%	$136.4512	$136.45	$136.45	$136.50
Purchase #2	$68.80	3.393%	$71.1344	$71.13	$71.15	$71.10
Purchase #3	$249.32	7.610%	$268.2933	$268.29	$268.30	$268.30
Purchase #4	$102.44	13.719%	$116.4937	$116.49	$116.50	$116.50
Purchase #5	$29.31	12.415%	$32.9488	$32.95	$32.95	$32.90
Purchase #6	$91.55	5.490%	$96.5761	$96.58	$96.60	$96.60
Purchase #7	$24.50	10.480%	$27.0676	$27.07	$27.05	$27.10
7 purchase totals =	$693.26		$748.9651	$748.96	$749.00	$749.00