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	$83.85	6.418%	$89.2315	$89.23	$89.25	$89.20
Purchase #2	$43.52	10.805%	$48.2223	$48.22	$48.20	$48.20
Purchase #3	$161.39	7.337%	$173.2312	$173.23	$173.25	$173.20
Purchase #4	$230.77	7.633%	$248.3847	$248.38	$248.40	$248.40
Purchase #5	$139.68	7.535%	$150.2049	$150.20	$150.20	$150.20
Purchase #6	$143.52	6.546%	$152.9148	$152.91	$152.90	$152.90
Purchase #7	$219.85	8.546%	$238.6384	$238.64	$238.65	$238.60
7 purchase totals =	$1,022.58		$1,100.8278	$1,100.81	$1,100.85	$1,100.70