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	$46.82	9.694%	$51.3587	$51.36	$51.35	$51.40
Purchase #2	$56.86	4.603%	$59.4773	$59.48	$59.50	$59.50
Purchase #3	$205.31	12.269%	$230.4995	$230.50	$230.50	$230.50
Purchase #4	$102.88	6.437%	$109.5024	$109.50	$109.50	$109.50
Purchase #5	$66.65	3.830%	$69.2027	$69.20	$69.20	$69.20
Purchase #6	$17.82	8.526%	$19.3393	$19.34	$19.35	$19.30
Purchase #7	$18.92	8.312%	$20.4926	$20.49	$20.50	$20.50
7 purchase totals =	$515.26		$559.8725	$559.87	$559.90	$559.90