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	$87.44	6.791%	$93.3781	$93.38	$93.40	$93.40
Purchase #2	$51.59	10.867%	$57.1963	$57.20	$57.20	$57.20
Purchase #3	$81.78	10.385%	$90.2729	$90.27	$90.25	$90.30
Purchase #4	$166.43	3.495%	$172.2467	$172.25	$172.25	$172.20
Purchase #5	$106.92	13.404%	$121.2516	$121.25	$121.25	$121.30
Purchase #6	$67.72	12.303%	$76.0516	$76.05	$76.05	$76.10
Purchase #7	$148.96	10.418%	$164.4787	$164.48	$164.50	$164.50
7 purchase totals =	$710.84		$774.8759	$774.88	$774.90	$775.00