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	$223.29	11.493%	$248.9527	$248.95	$248.95	$249.00
Purchase #2	$86.47	6.759%	$92.3145	$92.31	$92.30	$92.30
Purchase #3	$239.32	12.235%	$268.6008	$268.60	$268.60	$268.60
Purchase #4	$248.47	8.851%	$270.4621	$270.46	$270.45	$270.50
Purchase #5	$158.39	5.761%	$167.5148	$167.51	$167.50	$167.50
Purchase #6	$79.61	3.393%	$82.3112	$82.31	$82.30	$82.30
Purchase #7	$144.80	12.420%	$162.7842	$162.78	$162.80	$162.80
7 purchase totals =	$1,180.35		$1,292.9403	$1,292.92	$1,292.90	$1,293.00