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	$166.90	11.109%	$185.4409	$185.44	$185.45	$185.40
Purchase #2	$123.73	8.500%	$134.2471	$134.25	$134.25	$134.20
Purchase #3	$203.31	9.312%	$222.2422	$222.24	$222.25	$222.20
Purchase #4	$87.61	6.123%	$92.9744	$92.97	$92.95	$93.00
Purchase #5	$199.58	9.504%	$218.5481	$218.55	$218.55	$218.50
Purchase #6	$202.88	13.156%	$229.5709	$229.57	$229.55	$229.60
Purchase #7	$116.57	13.566%	$132.3839	$132.38	$132.40	$132.40
7 purchase totals =	$1,100.58		$1,215.4075	$1,215.40	$1,215.40	$1,215.30