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	$17.73	4.661%	$18.5564	$18.56	$18.55	$18.60
Purchase #2	$154.36	6.610%	$164.5632	$164.56	$164.55	$164.60
Purchase #3	$103.88	12.105%	$116.4547	$116.45	$116.45	$116.50
Purchase #4	$21.60	4.273%	$22.523	$22.52	$22.50	$22.50
Purchase #5	$52.96	8.864%	$57.6544	$57.65	$57.65	$57.70
Purchase #6	$73.69	13.524%	$83.6558	$83.66	$83.65	$83.70
Purchase #7	$212.76	3.347%	$219.8811	$219.88	$219.90	$219.90
7 purchase totals =	$636.98		$683.2886	$683.28	$683.25	$683.50