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	$19.40	7.803%	$20.9138	$20.91	$20.90	$20.90
Purchase #2	$95.25	9.575%	$104.3702	$104.37	$104.35	$104.40
Purchase #3	$242.43	10.426%	$267.7058	$267.71	$267.70	$267.70
Purchase #4	$137.27	13.392%	$155.6532	$155.65	$155.65	$155.70
Purchase #5	$196.49	11.851%	$219.776	$219.78	$219.80	$219.80
Purchase #6	$63.34	6.739%	$67.6085	$67.61	$67.60	$67.60
Purchase #7	$46.44	10.114%	$51.1369	$51.14	$51.15	$51.10
7 purchase totals =	$800.62		$887.1644	$887.17	$887.15	$887.20